By reading travel magazines, i have identified all of the amazing places i plan to visit after college.

which role does reading serve in the sentence above?

a.) object of the preposition
b.) subject of the sentence
c.) predicate nominative
d.) direct object of the verb

The correct answer among all the other choices is D.) direct object of the verb. This is the role that READING serves in the sentence given above. Thank you for posting your question. I hope this answer helped you. Let me know if you need more help. 

"Males who inherit the mutation get the disease because they have no second dystrophin gene to make up for the faulty one. Early in the embryonic development of a female, either the X chromosome from the mother (maternal X) or the one from the father (paternal X) is inactivated in each cell."

(courtesy https://www.mda.org)