Question

Tom___ China for 3 years. A. has been B. has been in C. has been to D. has been at

Answer 1

B. has been in
汤姆在中国三年了.

A 缺少介词, C , has been to 表示曾经去过, 不合句意.

D中的at表示在小地方, 在中国 用: in China.

Answer 2

have been to 表示去过……（某地），人已回来，常与once/twice/three times…等表示频率的词组连用，表示“去过某地多少次”。
have been in 表示一直在……（某地），人未离开，常与表示“一段时间”的词组连用，如：how long, for……， since……等