Keen on/at? phrasal verb usage Please help me fill and explain the following sentences. 1. You don't seem keen ____ playing tennis. My answer is keen on but I am not sure about the explanation. 2. She is keen ___ watch the movie. She is keen _____ watching the movie. For the first one, i think it is 'keen to' watch the movie. And for the second, I think it is 'keen on'. Can you let me know why the prepositions can change? Thank you!