问题补充：
_ I was the point of telephoning him when his letter arrived.
A. in
B. to
C. at
D. on
答案：
A. in
B. to
C. at
(答案→)D. on
解析：考查介词。on the point of doing sth.是固定搭配，另外注意这个句子中并列连词when连接的固定句型：on the point of doing...when...,意思是“正要干……这时……”，这样的句型还有 be about to do...when...,was doing...when...。
