如图所示，小球悬浮在水中，请在图中画出小球所受浮力和重力的示意图．

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关于细胞生长、分裂和分化的说法，正确的是（　　）

A：Hi，Bill！____.

B：Yes.I've already finished my homework.

A：____.

B：I'd like to work outside.

A：Me，too！____.

B：I'd like to do something to help others.Would you like to go with me?

A：Sure！Let's come up with a plan.____.In the afternoon we can visit the children's hospital to cheer up the sick children.What do you think?

B：____. But we had better join the school weekend volunteer program.

A：Good idea！We could do better then.