高压加热系统的（LAD）功用是什么？
参考答案：
用从汽轮机高压缸来的抽汽加热给水，收集从汽水分离再热器来的疏水；提高热效率。
.He was about to leave ______the telephone rang; ______was from his mother.
A．when; that
B．before; which
C．when; it
D．before; this
