单项选择题 在美国的商业票据市场上,大多数商业票据的发行面额都在( )。

多项选择题 引起水泥体积安定性不良的主要原因是熟料中含有过量的（）。

单项选择题 听力原文：M: Didn't I tell you? I retired on Friday.W: Really! I didn't think you'd be retiring for another five years or so.M: Well. I'll be seventy then, you know.W: Well. I never! I thought you were still in your fifties.How old is the man now?A．In his fifties.B．In his sixties.C．Seventy.D．Seventy-five.