I'm keen _____playing with my daugther in the park.

• A. In
• B. To
• C. On
• D. For

Answer: (C)

The key idea is how we pair adjectives with prepositions to talk about interests. With the adjective keen, a common and natural pairing is keen on + an -ing form, which expresses that you enjoy or are interested in doing something. Here, playing with my daughter in the park is the activity you’re enthusiastic about, so the natural fit is keen on playing.

Using a different preposition doesn’t fit standard usage: keen in isn’t a standard collocation, and keen to would usually precede a base verb (keen to play) rather than a gerund form like playing. Keen for would be odd in this context as well.

So, the best choice links keen to the activity by saying you’re keen on playing.