一般情况下，健康人的尿液中不含哪种成分（　　）

设函数f（x）= $\{\begin{array}{c}-x,x<1\\ {\left(x-1\right)}^2,x\ge 1\end{array}$ ，若f（a）=1，则实数a的值为（   ）

It's time      school.

家庭联产承包责任制是：

选择合适的句子补全对话。

A. It is Peter's bear.   B. Yes. It's my sheep.  C. Is this your bear? D. No, it isn't.   E. Whose goose is this?

A: Wow! What a big zoo!
B: Look at all the animals! They are so cute.
A: Oh. This is a bear.____
B: No, it isn't.____
A: Is that your sheep?
B:____
A:____ Is it your goose?
B:____ It's Lisa's goose.