问题补充：
—Sorry. I to post the letter for you.
—Never mind. it myself after school.
A. forget; I’d rather post
B. forgot; I’ll post
C. forgot; I’m going to post
D. forget; I’d better post
答案：
A. forget; I’d rather post
(答案→)B. forgot; I’ll post
C. forgot; I’m going to post
D. forget; I’d better post
解析：由道歉可知，当时“忘记”帮对方寄信了，forget应发生在过去；“放学后自己去寄”是临时的决定，只能用will而不能用表示计划或打算的be going to。
