After I left _______ Linchuan No.2 Middle School, I began college classes in _______  September 2010.   

A．a; the

B．不填; the

C．the; the

D．不填；不填

自然循环锅炉的下降管布置在炉墙外面的时候，必须用保温材料包上。这样既可减少锅炉的散热损失，也对锅炉的水循环有利。