单选题 Just as the value of a telephone network increases with each new phone ______ to the system, so does the value of a computer system increase with each program turned out.
A. adding B. to have added C. to add D. added

【正确答案】 D
【答案解析】四个选项中有两个是不定式，两个是分词。解此题首先要考虑空当中需填入不定式还是分词。假如知道在with+名词后一般跟分词而不跟不定式，那么就可以排除B、C。A和C的区别在于语态。新的电话机自然是由人并入电话网络，所以动词应是被动形式，因此答案显然是D。