—Students are supposed _______.
—I agree with you.
A:study hard
B:studying hard
C:to studying hard
D:to study hard
计算:1﹣(﹣13)=( )
①AD是∠BAC的平分线
②∠ADC=60°
③点D在AB的垂直平分线上
④AB=2AC.
关于亚洲海陆位置的叙述,错误的是( )