单项选择题
There is something wrong with our radar．All kinds of objects can’t be clearly（）within the definite range.
A.Shown B.Expressed C.Appeared D.Displayed
单项选择题 There is plenty of（）at this area.
单项选择题 The primary reason for placing covers over storage batteries is to（）.
单项选择题 The master should（）necessary precautions to prevent accidents or damage.
