海因里希事故连锁理论把事故发生过程概括为五个因素，对该五个因素的正确描述是( )。

A．管理缺陷；环境缺陷；人的不安全行为和物的不安全状态；事故；伤害
B．直接原因；遗传及社会环境；人的缺点；事故；伤害
C．基本原因；管理缺陷；人的不安全行为和物的不安全状态；事故；损失
D．遗传及社会环境；人的缺点；人的不安全行为和物的不安全状态；事故；伤害

A typical application of this (71) is ADSL. It is emerging as the technology for home-and small-office Internet connectivity. It provides either 1.5 Mb/s～8 Mb/s from the network to the user and 64 Kb/s～512 Kb/s in the reverse direction depending on the distance, 12 000 or 18 000 feet.. The different speed for each direction gives it the (72) label. ADSL is designed to take advantage of the fact that video-on demand, telecommuting, and Internet access traffic are inherently asymmetrical. The user (73) a brief message up to the network and receives a ton of data coming back, either a movie or a piece of data download. Under such a scenario, low-speed traffic to the network is just fine. ADSL delivers high (74) where you need it and only uses a single copper pair. Through multiplexing, it also reserves (75) of the bandwidth for POTS.

A．channel

B．computation

C．speed

D．bandwidth