牙发育沟上呈“+”字形的牙为（）
A.上颔第一磨牙
B.上颌第二磨牙
C.下颌第一磨牙
D.下颌第二磨牙
E.上颌中切牙
参考答案：D
--- Is the boy ______ is _______ food and clothes over there a volunteer? ---Yes. He is very kind.
A．which; set up
B．that; put out
C．whom; handing out
D．who; giving away
在郊区，公共汽车的大站快车的站距是( )。
A．1000～1500mB．1000～2000mC．1500～2000mD．1500～2500m
