令ha（t)，sa（t)和Ha（s)分别表示一个时域连续的线性时不变滤波器的单位冲激响应，单位阶跃响应和系统函数。令h（

已知某地区设计重现期为5年、25年、50年的5min暴雨强度分别为240L／（s·ha)， 1050L／（s·ha)和2000L／（s

高压给水系统、管网上消火栓出口压力公式为：H栓=T＋H＋ha，其中ha表示的是（)。A.消火栓出口压力B.消火

Doing morning exercises has helped to improve her health, ______？A．isn"t itB．hasn"t itC．ha

I______to him because he phoned me shortly afterwards.A．ought to have writtenB．couldn"t ha

_____, the boy couldn’t get into his dorm. A. Since the key lost B. The key ha

我妹妹今天没去上学。她得了重感冒，头痛，发烧。 My sister doesn’t go to school today. She ha