David is ____ an E-mail to his father.填空题.

问题描述:

David is ____ an E-mail to his father.填空题.

此处可以有多种填法,但一定是进行时,表示David正在做什么,而且必须表示持续的.个人感觉此处应填writting,表示David正在给他父亲发邮件