已知实数x，y满足x2+y2+4y=0，则s=x2+2y2﹣4y的最小值为[ ]
A．48
B．20
C．0
D．﹣16
答案：C
厂房、设备、容器应按什么要求制订清洁规程？
—Were you pleased with her answer?
--Not at all. In fact it couldn’t have been______.
A．worse
B．so better
C．better
D．the worst
