一个三角形三个内角的度数之比是2∶3∶5,则这个三角形一定是( )
A:直角三角形
B:等腰三角形
C:钝角三角形
D:锐角三角形
下面句子中标点符号使用正确的一项是( )
Hello ! My name is LiQiang . There are four people in my family . My father is a worker . My mother is a farmer . My little sister is a pupil. I am a pupil , too . We are in the same school .
已知函数fx=-x3+ax2-x-1在-∞,+∞上是单调函数,则实数a的取值范围是( )