I had promised to send him an email I got home but I was so busy that I forgot to do so .A

问题补充：

I had promised to send him an email I got home but I was so busy that I forgot to do so .

A. while

B. until

C. the moment

D. ever since

答案：

A. while

B. until

(答案→)C. the moment

D. ever since

解析：这题考查连词的用法：the moment“一…就…”，句意是：我许诺一到家就给他发一份E-mail，但我太忙忘了。选C。