Parallelism, or parallel structure, is a grammatical device that makes sure your comma series match up with verb and subject. you want your verb tenses to match, and it's best to keep it in the same order; if your subject is first, list the subject first for every list item; if your verb comes first, list it first for every list item. basically, parallel structure asks you to make everything look uniform.
choice A -- "do my homework," "mow the yard," and "help mom with dishes" are all in the same format. "do," "mow," and "help" are all present-tense verbs, and the subjects of those verbs follow. this sentence correctly uses parallelism.
choice B -- "running track" to "playing football." you have verbs ending in -ing followed by specific sports. this sentence correctly uses parallelism.
choice C -- "drove to school," "went to play rehearsal," and "the play was wonderful." this sentence doesn't read well. try reading it out loud, and notice that the last part of the sentence doesn't flow as well as the first two pieces in the comma series. "the play was wonderful" is not parallel; it should have the past-tense verb first (just like "drove" and "went") and finish up with the subject. instead, it has the subject, followed by a verb and an adjective.
choice D -- "we have great players" but "we do not work as a team." these are parallel and they match up. it begins with "we" as the subject then follows with verbs "have" and "work."
