登记账簿必须以账产为依据，利用复式记账的方法，将经济业务分门别类地登记到账簿中去。（）
参考答案：错
He is rather difficult to make friends with, but his friendship, ____, is more true than any other.
A．once gained
B．when to gain
C．after is gained
D．while gaining
50dB的声音与30dB的声音迭加结果约为（）dB。
A.80
B.50
C.40
D.30
