热带的气候情况是( )
A:终年炎热,有太阳直射的现象
B:终年寒冷
C:四季变化明显
D:不冷不热
已知 {an} 为等差数列, Sn 为其前n项和,若 a1=6 , a3+a5=0 ,则 S6 =____
We don't want to speak badly or ______ in front of the class.
下列计算错误的是( )