He had to retire(退休) early poor health.A. as a resultB. becauseC. soD. because of

问题补充：

He had to retire(退休) early poor health.

A. as a result

B. because

C. so

D. because of

答案：

A. as a result

B. because

C. so

(答案→)D. because of

解析：连词考查。Because与because of都表示原因，但because必须引导句子，而because of后跟名词。