Mr. Smith works as a government official now, but he ____________ in a middle school for 5 years.

A．has worked

B．worked

C．had worked

D．had been working

患者，女，27岁，孕38周，前置胎盘，检查时发现子宫增大至足月大小，鲜红血液从产道流出。

若选用脊麻，最易发生的并发症为（）。

A.头痛

B.低血压

C.子宫松弛

D.尿潴留

E.术后腰痛