单项选择题
The defective places in the furnace （） with fire bricks.
A.should be paved B.should be cleaned C.should be dismantled D.should be welded
单项选择题 After fitting back in place the gear wheels, don’t forget to （） them.
单项选择题 What separate the high pressure side from the low pressure side in a refrigeration system?（）
单项选择题 Which of the following best describes “overcharge of refrigerant”?（）
