下列计算,正确的是
A:--3=-3
B:30=0
C:3-1=-3
D:9=±3
把问题和答语对应起来。
A.He's from China.
B.He's my teacher.
C.No, she is old.
D.He's short and thin.
E.No, he is old.
下列哪项是腔肠动物和扁形动物的共同特征( )