单项选择题
When the heat load begins to increase, the needle valve of an expansion valve will（）
A.move in an opening direction B.move in a closing direction C.either open or close D.not move at all
单项选择题 One of the main purposes of refractories in a boiler furnace is to（）
单项选择题 What is the first thing you would check on taking over a watch?（）
单项选择题 Soot blowers should be used in proper sequence so that（）
