新管线在引用蒸汽前，应当缓慢引入，并且充分脱除凝结水。
参考答案：对
This is the first time that I face to face with the president.
A．had come
B．have come
C．came
D．come
环境中哪一种污染物不易引起持续性蓄积危害
A．DDTB．氰化物C．PCBD．镉E．铅
