血清病通常发生于异源血清注射后（）
A.即刻
B.数小时内
C.1～3天
D.3～5天
E.6～10天
参考答案：E
He failed in finding the job. I think that he _____to get some
more qualifications before applying for the job.
A．should have tried
B．must have tried
C．might have tried
D．needn’t have tried
简述企业福利的种类。
