The Smiths         many places of interest since two years ago.

In our school library there          a number of books on science, and in these years the number of them          growing larger and larger.

在⁴⁰₂₀Ca中，质子数为 ____，中子数为　 ____，电子数为　 ____；画出该原子的原子结构示意图　 ____，它在元素周期表中的位置是第 ____周期　 ____族，它的最高价氧化物对应水化物的化学式是 ____

写出下列单词的过去式。

( 1 )sleep____   ( 2 )have____

( 3 )read____   ( 4 )watch____  

( 5 )drink____   ( 6 )stay____  

( 7 )wash____   ( 8 )play____  

( 9 )clean____  ( 10 )do____