Select the sentence that illustrates the proper use of parallel structure. (5 points)

a
Tomorrow I have to walk the dog, writing an essay, and mail a letter.

b
Tomorrow I have to walk the dog, write an essay, and mail a letter.

c
Tomorrow I have to walk the dog, write an essay, and I have to mail a letter.

d
Tomorrow I have to walk the dog, to write an essay, and mail a letter.