Well it is difficult to tell for you tell that the girl is interested in you. I know that I'm interested in a girl who I know because we're in the same honor society. I'm just building our friendship first till she mentions that she wants us to be more than friends. Girls can figured out that you're interested in them because they are very good at reading body language.
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"You are the stars and the world is watching you. By your presence you send a message to every village, every city, every nation. A message of hope. A message of victory."- Eunice Kennedy Shriver