牙本质龋最深层的改变是（）
A.脂肪变性层
B.透明层
C.脱矿层
D.细菌入侵层
E.坏死崩解层
参考答案：B
Very ______ about toys, Tony was not to be pleased, though I tried to show him one by one.
A．responsible
B．particular
C．special
D．curious
对于顶置式气门配气机构而言，气门间隙是指（）的间隙。
A.气门杆尾端与摇臂撞头之间
B.气门杆尾端与挺柱之间的间隙
C.活塞环开口
D.挺杆与摇臂之间
