问题补充：
---Did a letter come for me?
---Yes, came for you when I was on the point of going out this morning.
A. that
B. it
C. one
D. this
答案：
A. that
B. it
(答案→)C. one
D. this
解析：代词用法考查题。That可代指不可数名词或者可数名词单数后边往往有定语修饰；it代指同一物；one代指可数名词单数相当于a +单数名词。“有我的信吗？”“有，今天早晨我刚要出去这时你的一封信到了”选C
