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一、填空题1.如图1,直线a、b被直线c所截,若要使a∥b,需增加条件:___(填一个即可).
First, fill in the blank 1. As shown in Figure 1, a straight line b, b is cut off by a straight line c, to make a∥b, the need to increase the conditions: ___ (fill in a can).