问题补充：
Mr. Read is the person to you should write.
A. whom
B. who
C. which
D. that
答案：
(答案→)A. whom
B. who
C. which
D. that
解析：考察定语从句。本题的先行词是the person，句中的whom指代先行词作为介词to的宾语。固定搭配write to sb写信给sb。本题只是把to提前放在关系代词的前面。Who在定语从句中通常做主语，只在非正式情况下才做宾语。Which的先行词不能是人。That通常不能放在介词的后面。故A正确。
