(     ) Let's put the magnet (磁铁)near the nails.      

如图所示，把一个底面积为S，高为l的长方体浸没在密度为ρ的液体中，上、下表面分别距液面为h₁和h₂，因为液体内部存在压强，所以长方体各表面都受到液体的压力．

阅读下面短文，从各题所给的A、B、C、D四个选项中，选出最佳选项。

    Jack and Mike are on holiday in France. Mike loves visiting old buildings. Jack likes, too. In the village Jack and Mike see a beautiful old church, but when they come into the church, some people are there. They don't know what the people are doing .

    "Oh! Just sit quietly, and do like the others!" Mike says. Because they don't really know French, so they stand, kneel, and sit to follow other people.

    Then the priest(牧师)says something. The man next to Jack and Mike stands up. "We should stand up, too!" Jack whispers to Mike.

So, Jack and Mike stand up with the man. Suddenly, all the people smile! After that, Jack and Mike walk to the priest. "What's so funny?" Jack asks in English. With a smile on his face the priest says, "Boys, there is a new baby born, we ask the father to stand up."Mike smiles and says, "We should understand what people do before we do like them. "

关于胰岛素的叙述，下列何者正确？（  ）