The thermostatic valve has a throttling action, that is to say the valve can（）

单项选择题When the refrigeration demand is small,（）

A.the expansion valve will move toward the wide open position
B.the expansion valve will move toward the closing position
C.the feeler bulb will conveys the high temperature
D.the superheat degree will raise

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（）

A.help preheat the air for the furnaces
B.help preheat the feedwater
C.protect economizer from excessive heat
D.prevent excessive furnace heat losses

单项选择题What is the first thing you would check on taking over a watch?（）

A.the bilges
B.the periscope
C.the water level
D.the oil pressure

单项选择题Soot blowers should be used in proper sequence so that（）

A.excess stresses will not be set up in the boiler
B.the decks will not be covered with soot
C.the soot will be swept toward the uptakes
D.there will not be a loss of steam pressure