I don't practice karate.
I used to practice karate, but now...
I don't play with the yoyo.
I used to play with the yoyo, but now...
I don't sing.
I used to sing, but now...
I study Science.
I didn't use to study Science, but now...
I don't paint.
I used to play, but now...
I study Physics.
I didn't use to study Physics, but now...
I don't play the piano.
I used to play the piano, but now...
I study Biology.
I didn't use to study biology, but now...
I don't play.
I used to play soccer, but now...
I study Literature.
I didn't use to study Literature, but now...
I study Chemestry.
I didn't use to study Chemestry, but now...