人体内维生素A的主要活性形式有()
A.9-顺式视黄醛
B.9-反式视黄醛
C.9-顺式视黄酸
D.11-顺式视黄醛
E.11-反式视黄醛
参考答案:A, D
We've just moved into a bigger house and there's a lot to do. Let's ________ it.[ ]
A. keep up with
B. do away with
C. get down to
D. look forward to
车站应设在线路平道、直线的()处。
A.前段
B.中点
C.适当
D.宽阔