如果□×3ab=3a2b，则□内应填的代数式是（ ）
A：ab
B：3ab
C：a
D：3a
读句子，将问句和答句连线。
①What’s the matter?____ A. Thank you.
②Let me help you. ____ B. Me, too.
③I have yellow hair. ____ C. My name is Mike.
④Do you hurt your hand?____ D. Yes, I do.
⑤What’s your name?____ E. I hurt my foot.
