Which sentence uses punctuation correctly?

a.
There are many ways to be productive on a rainy afternoon; Reading is my favorite way to pass the time.

b.
There are many ways to be productive on a rainy afternoon; reading is my favorite way to pass the time.

c.
There are many ways to be productive on a rainy afternoon, reading is my favorite way to pass the time.

d.
There are many ways to be productive on a rainy afternoon - reading is my favorite way to pass the time.