引起血吸虫病的血吸虫中间宿主为（）。
A、蛙
B、鱼
C、螺
D、贝
参考答案：C
—Do you often ______ your sister?
—Yes, she often writes to me. [ ]
A. hear
B. hear of
C. hear from
D. hear about
当路面混凝土抗压强度不小于（）MPa方可拆模。
A、4.0
B、8.0
C、12.0
