药材大黄主要含有的化学成分类型是（）
A.生物碱类
B.皂苷类
C.蒽醌类
D.挥发油类
E.强心苷类
参考答案：C
It was in the factory _______ his friend worked _______ he picked up a lot of experience.
A．where, where
B．that, where
C．that, that
D．where, that
从事科研、设计等工作的人员不会形成职业病。
