根据句意及首字母提示完成单词
We went to a summer c____ last year.
There w____  many trees on the mountains five years ago(以前).
We are studying hard for e____ .
—He was an English teacher.—R____ ?  Did he teach you?
What an a____  classroom!  It’s too dirty!

 “一滴水中约有1.67×10²¹个水分子”说明了（　　）

多音字组词

汗hán____     hàn____     

奔bēn____     bèn____

下列有关声现象的说法，正确的是（  ）