Mary plays light music _________ her free time to enjoy the beauty of music.
in
at
on
There _____ a number of people at the square in the morning, the number _____ over 1,000.
I _____________ his letter for a week.
We will go climbing _______ it ________ tomorrow.
My mother _______________ my aunt called her.
He is _______ clever boy that he can solve _____ many difficult problems.