词型转换：用括号中所给单词的适当形式填空。(共5小题；每小题2分，共10分）

小题1:The bus is ________ (crowd) . Let’s get on it .

小题2:I won’t believe in you unless you tell me the ________ (true).

小题3:Kangaroos are playful and polar bears are __________ (fur).

小题4:You are supposed to type ________ (quick) when you are chatting online.

小题5:Take the elevator to the _________ (nine) floor, you can find it.

“食盐加碘”、“酱油加铁”、“儿童补钙”等，这里碘、铁、钙指的是

A．原子

B．元素

C．分子

D．离子