直接引语变成间接引语,用if还是whether引导?还是必须用if?

问题描述:

直接引语变成间接引语,用if还是whether引导?还是必须用if?
“will Jimmy write a letter to me?” Grandmother asks Penny.

= =其实都可以.
建议用whether.因为一旦出现‘or not’,就只能用whether.