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Public Wi-Fi Users Neglect SafetyA recent survey shows that 25% of Internet users have done online banking through public Wi-Fi in the last three months. It also shows that 27% have bought a product or service with a credit card this way.Experts worry that hackers (黑客) will take advantage of these practices. Doug Shadel said that hackers usually attack in two ways. They may create Wi-Fi hotspots that have the same name of the ones you trust, such as a hotel or a coffee shop. They may also provide a stronger Wi-Fi signal to get between you and the safe hotspot. In either case, the hackers can see your email, credit card information, user names and passwords.Sometimes hackers just set up their electronic traps near a business where people enjoy the free Wi-Fi. “In most cases they are after your personal information, Shadel said.“If you use the same user name and password for many accounts, they can get into them all. It's possible for any hacker to do it. The software to hack into a Wi-Fi network is available at little or no cost."“It's difficult for people to know if a Wi-Fi network is safe," Shadel said. “So you should just think they are not. Any shared Internet access, free or paid, carries the same level of risk. It is safe only when you or someone you trust directly controls it."Shadel sometimes checks email through public Wi-Fi. But he never does any banking that way. In an unfamiliar place, he uses a Virtual Private Network (VPN).“This service creates a passage between your device and a safe place on the Internet," he said.1. A recent survey finds that 25% of Internet users use public Wi-Fi to_ .2. The phrase“take advantage of” (Para. 2) can best be replaced by “_ ”.3. According to Shadel, any hacker can_.4. For the sake of safety, Internet users are advised to_.5. Shadel uses public Wi-Fi to___.

Why Dogs Bury Their Favorite BonesYou may find it crazy that your dog buries his favorite bone or chew toy, only to dig it up a day or two later, but there is actually a reason behind it -it is simply in their nature. For thousands of years, dogs have buried their bones. The practice itself started long before dogs were even pets when they had to bury bones to survive.When dogs lived in the wild, sometimes food was scarce. If they were able to find food, dogs became very protective of it. Sometimes they would have more bones than they could eat for one meal. To keep other dogs and animals from stealing their bones, dogs would bury them in the ground. When it was time for the next meal, they would dig up their bones and enjoy them again. This would continue until the bones were gone.Even though most dogs have plenty of food to eat today, their instincts still tell them to bury their bones and favorite toys. They do this to keep other dogs and animals from stealing them, just like their ancestors did. Some dogs keep at least two bones buried at once. When they want to dig up one, they will bury one more. This may leave a backyard full of holes and bones.How do dogs decide where to bury their bones? A dog cannot bury a bone just anywhere. He must first find the perfect spot. This involves using his nose to find a spot that is free from other dogs and animals. Often it is near a tree or a large rock, but it could be anywhere in the yard. Once the dog finds the perfect spot, he uses his front paws to dig a hole, drops the bone in and covers up the hole to protect his treasure.1. Dogs bury their favorite bones or chew toys by nature.2. Dogs started to bury their bones when they became pets.3. Dogs in the wild occasionally had enough food.4. Dogs would bury their extra food for their babies.5. Animals would start a fierce fight over food in ancient times.6. Some dogs tend to store up more than one bone at the same time.7. The backyard of a dog owner may be full of holes dug by his dog.8. Dogs often bury their bones far away from trees.9. Dogs use their paws to find spots for burying bones.10. Dogs bury more bones than chew toys.

如图，一根长直导线中通以I=50A的电流。在距导线9.0x10-2m的A处放置一个面积为1.0x10-5m2的小导体环（环中的磁场可看成是均匀的），导体环与长直导线共面。已知μ0=4πx10-7N·A-2，若在0.020s时间内把此环沿垂直于导线的方向从A处移到B处，

如图，两个偏振片P1、P2平行放置，其偏振化方向之间的夹角为30°，一束强度为I0的光垂直入射到偏振片上，测得连续透过两个偏振片后的出射光强为。已知该入射光由强度相同的自然光和线偏振光混合而成，求入射光中线偏振光的光矢量方向。

分别求空气（视为刚性双原子分子理想气体）在下列准静态过程中热力学能的改变量和吸收的热量。已知各过程中空气对外做功均为200J。（摩尔气体常量R=8.31J·mol-1·K-1）

物体在黏性流体中运动时，会受到流体的阻力，当速率不太大时，球形物体在水中受到的阻力为F= 6πηrv，式中r为球的半径，v为其速率， η为水的黏度。现有一质量为m，半径为R的球体，在水中由静止释放后下沉，已知水的密度为ρ。求：

一质量为m，电量为q的粒子，由静止经加速电压U加速后，其德布罗意波长为_____。（普朗克常量为h，不考虑相对论效应）

一质量为0.1 kg的物体做简谐振动，周期为4πs。物体在距平衡位置0.04 m处所受的合外力的大小为_____N。

一电子以一定的速度进入均匀磁场，进入磁场时的速度方向与磁场方向的夹角为θ，该电子在磁场中运动的轨迹是_____。（选填“直线”、“圆”或“螺旋线”）

1 mol的氢气（视为刚性双原子分子理想气体）经绝热过程后，温度降低了△T，则热力学能变化了_____。（摩尔气体常量为R）

已知地球质量为M，半径为R，万有引力常量为G。质量为m的卫星绕地球做圆周运动，距地面高度，则其势能为_____。（取无穷远处势能为零）

一质点沿半径为R的圆周运动，其角坐标随时间t变化的规律为θ=2+t2(SI)，则t时刻质点的法向加速度为_____。

电子的动能为Ek时，其德布罗意波长为λ。当该电子的动能增大为4Ek时，电子的德布罗意波长为（不考虑相对论效应）（）。

真空中，惯性系S’相对于惯性系S以0.5c的速度沿x轴负方向运动，若从S’系的坐标原点沿x轴正方向发射一光子，则在S系中测得该光子的速度为（以c表示真空中的光速）（）。

设某微观粒子的总能量是它的静止能量的n倍(n>1)，则其运动速度的大小为（以c表示真空中的光速）（）。

某元素的特征光谱中含有波长分别为λ1=450nm和λ2=750nm的光谱线。在光栅光谱中，这两种波长的谱线有重叠现象，重叠处λ2的谱线的级数可能是（）。

在x轴上有两列波长为λ=4.0cm的简谐波叠加形成驻波。若x=0处为波节，则（）。

一平面简谐波沿x轴负方向传播，角频率为w，波速为u，周期为T。设时刻的波形如图所示，则该波的表达式为（）。

一简谐振子的振动方程为x= A0cos(wt +φ)，式中（）。

下列说法正确的是（）。

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