He earned enough money to start his own business _____ offering guide services _____ tourists.
A.by; to
B.with; at
C.on; for
D.through; with
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A解析介词by可以表示手段、原因,常置于动名词前,如:You can make the cake by mixing eggs and flour. 其次考查介词与动词offer的搭配,offer sth. to sb. = give sth. to sb.其中的to表示对象。