运动员用船桨向后划水时皮划艇就会向前运动，那么使皮划艇前进的力的施力物体是(　　)

关于物体的内能，下列说法中正确的是（  ）

谦虚____（骄傲；谨慎）

善良____（友善；凶恶）

幸福____（痛苦；烦恼）

清澈____（清亮；浑浊）

为了探究“电磁铁的磁性强弱跟哪些因素有关”，小欣所在的实验小组进行了

如下实验：用漆包线分别在两颗大铁钉上面绕制若干圈，做成简易电磁铁，然后分别按图接入电路．探究前，他们还作了以下的猜想：

猜想A：电磁铁通电时有磁性，断电时没有磁性；

猜想B：通过的电流越大，磁性越强；

猜想C：外形相同时，线圈的匝数越多，磁性越强．

探究过程如图所示：他们通过观察简易电磁铁吸引大头针的情况来判断磁性的有无和强弱，请你仔细观察这四幅图，然后完成下列填空．

（1）实验中他们是根据电磁铁是否吸引大头针来判断电磁铁是否具有磁性，同时根据____ 来判断电磁铁磁性的强弱．

（2）比较图____ ，可以验证猜想A是正确的．

（3）比较图____ ，可以验证猜想B是正确的．

（4）比较图____ 可以验证猜想C是正确的；但仔细分析发现，猜想C的表述还不完整，还应补充条件____ 

（5）滑动变阻器在电路中的作用是____ 和____ 

     If you have dinner with people in the west, I think you must pay more attention to the table manners. Here are some good table manners for you.
     When you eat something, try not to make a noise or burp (打嗝) at the table. Because people think that is not polite. People will say “Excuse me” when they want to burp.
      Talking with food in the mouth is very rude. So you must eat the food quietly and slowly. If you eat too fast, people think you are rude too. Do not talk with others when you have food in your mouth.
      It is good to eat all the food on your plate. This means you like the food very much. Remember to say the food is nice. And this can make the host very happy. When you finish eating, you can place your knife and fork together.