低位热值是指燃料完全燃烧，燃烧产物中的水蒸气以液态存在时的发热量。
参考答案：错
By the time he realizes he _____ into a trap, it'll be late for him to do anything about it．
A．walks
B．walked
C．has walked
D．had walked
魏氏组织主要出现在（）的焊接热影响区的过热区部位。
A.中碳钢
B.耐热钢
C.低碳钢和低合金钢
D.高合金钢
