大体积混凝土应采用（）振捣。
A、外部振动器
B、振动台
C、内部振动器
D、振捣棒
参考答案：D
—I’m sorry to have kept you waiting long.
—Never mind. I _____ here for only a few minutes. [ ]
A. have been
B. have come
C. have arrived
D. waited
开放式基金应保持足够的现金和流动性高的资产应付赎回。( )
