工伤保险实行什么（）原则。
A.固定费率
B.差别费率
C.浮动费率
D.基准费率
参考答案：B, C
______ has recently been done to improve the conditions of elementary schools, a great number of children are unable to go to school.
A．That
B．What
C．In spite of what
D．Though what
卖出看跌期权的最大潜在损失是（）。
A.获得的权利金
B.无限
C.行权价格
D.无法确定
