若x=$\sqrt{3}$+1，y=$\sqrt{3}$-1，则$x^2-y^2$的值为（    ）

随着生活水平的提高，人们对食品安全和食品污染等问题日益关心．下列对食品问题的看法中，正确的是（  ）

完成表格, 每空一词。

    You must hear about earthquakes, but do you know what to do during and after an earthquake? Here is some advice for you:

Before an earthquake. It is necessary to prepare yourself and your family. All family members should know how to turn off gas, water and electricity and know useful telephone numbers (doctor, hospital, police, 119etc). Never put heavy things over beds.

During the earthquake. It's important for each of you to stay calm. If you are indoors, quickly move to a safe place in the room such as under a strong desk or a strong table. It can protect yourself from falling things. Stay away from windows, large mirrors, heavy things and so on. If you are cooking, turn off the gas.

    If you are outdoors, move to an open area like a playground. It's important to move away from buildings, bridges and trees. If you are driving, stop the car as soon as possible. Stay in your car.

After an earthquake. Once the shaking stops, do not run out of the building at once. It's better to wait and leave when it is safe.

Check around you and help the people in trouble. If your building is badly broken, you should leave it. If you smell or hear gas, get everyone outside and open windows and doors. If you can do it safely, turn off the gas. Report it to the gas company.