麻黄升压的有效成分是()
A.右旋去甲基麻黄碱
B.麻黄碱
C.伪麻黄碱
D.1-α-松油醇及2,3,5,6-四甲基吡嗪
E.左旋去甲基麻黄碱
参考答案:B
He hasn't got any hobbies—_______ you call watching TV a hobby.[ ]
A. If
B. Unless
C. When
D. Since
供电电压的质量表现在哪几方面?