口服生蛋清会引起哪一种维生素的缺乏（）。
A.泛酸
B.核黄素
C.硫胺素
D.维生素D
E.生物素
参考答案：E
--- Why did you buy two pairs of shoes?
--- It was so hard to choose which was________, so I took them both.
A．better
B．the better
C．worse
D．the worse
在对机动链锯停机时，要失怠速运转（）分钟，再关停。
A.1
B.3
C.5
D.7
