会计记账采用借贷记账法。表外账可采用（）式记账法，以“收入”、“付出”为记账符号。
参考答案：单
The surroundings of his house _____ clean now. [ ]
a. is
b. are
c. was
d. were
PC机硬件在逻辑上主要由CPU、主存储器、辅助存储器、输入/输出设备与( )五类主要部件组成。
A．运算器
B．总线
C．显示器
D．键盘
