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
位于四川盆地西部的平原是( )
____
如图所示,起重机将重6×103N的货物匀速提升10m,再水平移动10m后静止,起重机在整个过程中对货物做功为 ____ J;若起重机的机械效率为80%,则起重机做的额外功为 ____ J.