精子属于
A．异嗜性抗原B．同种异体抗原C．自身抗原D．肿瘤抗原E．半抗原
参考答案：C
Be careful ____your things when you are on the train.
A. to B. with C. in
警察具有阶级性和社会性相统一的特点。 ( )
