Since he came to Beijing, he _____very happy. A is B has been C was D had been

题目

Since he came to Beijing, he _____very happy. A is B has been C was D had been
请问这道英语单选选哪个呢?哪位老师达人知道希望告诉我一下.
请告知为什么选那项,别的为什么不选?最后还请翻译一下这句话.多谢多谢~~~.

答案

B 一般since 引导的句子和for+段时间后面都跟完成时态