Password is a(n) (1) series of characters that enables a user (2) a file, computer or program. On multi - user systems, (3) user must enter his or her password (4) the computer will respond to commands. The password helps ensure that unauthorized users do not access the computer. In addition, data files and programs may require a password.

Ideally, the password should be something (5) could guess. In practice, most people choose a password that is easy to remember, such as their name or their initials. This is one reason it is relatively easy to break into most computer system.

4（）

A．after

B．when

C．while

D．before

煤的挥发分指标对锅炉燃烧的影响是（）。

A.挥发分指标与锅炉燃烧无关系；

B.挥发分越低，锅炉燃烧越稳定；

C.挥发分越高，着火越困难；

D.挥发分指标越高，越容易着火，锅炉燃烧越稳定。