急性喉炎易发生喉阻塞的年龄段是
A．1～6个月的婴儿
B．6个月至3岁的儿童
C．3～12岁的儿童
D．成人
E．老年人
参考答案：B
下列一元二次方程无解的是[ ]
A.x2-2x+1=0
B.x2+3x-2=0
C.2x2+x+3=0
D.2x2-3x-1=0
The final exam is a battle _______ everybody wants to show off his or her talent.
A．that
B．what
C．where
D．when
