采用双层缸有利于减小（），改善启动性能。
参考答案：汽缸内外壁温差
Neither Jam nor his parents _______ places of interest here since they came to China.
A．will visit
B．has visited
C．have visited
D．visited
隋唐时期大规模开凿的世界最大的艺术宝库是。
A．龙门石窟
B．云冈石窟
C．莫高窟
D．麦积山石窟
