Question

I think it is B:

Select the sentence that illustrates the proper use of parallel structure.

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

Answer 1

Yup it's B, don't get confused between writing in A and write in B.

Answer 2

The answer is B!

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