第25题: [单项选择]Smoking in bed on a ship is prohibited(). A. at all times B. during evening hours C. unless another person is present D. during drilling operations 参考答案:A
第33题: [单项选择]m=-1是直线mx+(2m-1)y+1=0和直线3x+my+3=0垂直的______. A. 充分而不必要条件 B. 必要而不充分条件 C. 充要条件 D. 既不充分也不必要条件 参考答案:A 答案解析:[解析] 直线mx+(2m-1)y+1=0和直线3x+my+3=0垂直的充要条件是3m+m(2m-1)=0,解得:m=0或m=-1,则m=-1是直线mx+(2m-1)y+1=0和直线3x+my+13=