His parents were worried that he______ too much time chatting on line.
A:spent
B:cost
C:paid
D:had
如图是某校九年级部分男生做俯卧撑的成绩(次数)进行整理后,分成五组,画出的频率分布直方图,已知从左到右前4个小组的频率分别是0.05,0.15,0.25,0.30,第五小组的频数为25,若合格成绩为20,那么此次统计的样本容量和本次测试的合格率分别是( )
下列各句中,没有语病的一项是( )
函数y=1-lnx1+lnx的导数是 ( )