This river forms a natural _______ between China and Korea.
A、boundaryA
暂无解析
The _______ work continued for more than a week but there was still no sign of the missing boy.
After working for twenty hours without any rest, the doctors were _______.
Whenaspacecrafttravels,oneofthemajorproblemsisreentryintotheEarth’s_______.
We can not trust him any more because he often________ his duty.
Whenmakingmoderncameras,peoplebeganto_______plasticsformetal.
