Documentation of a software package is normally produced for two purposes.One is to explain the(1)of the software and describe how to use them.This is known as (2)because it is designed to be read by the user of the software.The other purpose of documentation is to describe the software's intemal composition so that thesystem can be maintained later in its life cycle.Documentation of this type is known as(3)

空白（3）为（）

A.system documentation

B.user documentation

C.vender documentation

D.license documentation

项目投资回收期在一定程度上显示了资本的周转速度。资本周转速度愈快，回收期愈短，风险愈小，盈利愈多。下列选项不属于投资回收期缺点的是( )。

A．投资回收期只考虑投资回收之前的效果
B．投资回收期可以反映投资回收之后的情况
C．无法准确衡量方案在整个计算期内的经济效果
D．投资回收期作为方案选择和项目排队的评价准则是不可靠的