Feed a line - You cannot feed someone a line, can you? Imaging you are in a problem, and you need to make an excuse otherwise the punishment can be really big. Then it looks like that to evade the problem, you are feeding the person who is causing you the problem with that excuse, so we call it to feed a line. Feed a line means to tell someone something which is not exactly true, but moreover it is an excuse to evade the problems.
1. I am thinking about what to feed Mr. Helena, she will eat me if I tell her that I have not done the homework.
2. If she has not done the thing which I had asked her to do, I am sure she will feed me a line.
3. I am not feeding you a line, it's the fact.