安全经济效益评价是安全投资经济性评价的指标之一，其定义应该是投资收益（）投资费用。
A.除以
B.减去
C.加上
D.乘以
参考答案：B
— Where did you find your lost pen?
— It was in the park ____ we visited that day ____ I found it. [ ]
A. what; that
B. which; that
C. where; that
D. when; that
成熟红细胞的寿命为 （）
A.60天
B.70天
C.80天
D.100天
E.120天
