GMAT Sentence Correction (SC) | Re: While many students of foreign languages start out with the best of in

While many students of foreign languages start out with the best of intentions, many learners quickly discover thatthe effort involved in memorizing endless vocabulary words and doing countless drills are daunting.

A. theeffort involved in memorizing endless vocabulary words and doing countless drillsare daunting(Effort is Singular. Therefore usage of 'are' is wrong)
B. the efforts involvedin the memorizing of endless vocabulary words and doing countless drills are daunting (Between D and
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