Tom could swim very well at the age of seven.      [ ]

A. at he age of seven    

B. at his age of seven

C. when she was seven    

D. when he was seven

完成下列反应的化学方程式．

（1）氯化铵晶体和熟石灰混合研磨生成氯化钙和水，同时生成有氨臭味的气体

（2）炼铁高炉中生成铁的反应

（3）生石灰用作食品包装袋内的干燥剂

（4）铝片与硫酸铜溶液反应