Mayank and Line Segments

Mayank is very fond of geometry. He already knows about the general equation of line i.e. ax+by+c=0, where a,b and c are coefficients and x and y are variables. Today, He learned about the parallel lines. The parallel lines are the lines that will never meet at any point. Read more on Wikipedia. Now he has a set of N lines. There can be many subsets of this set in which all the lines are parallel