Question 36: Mark the letter A, B, C, or D on your answer sheet to indicate the undelined part that needs correction in each of the following questions: Since vitamins are contained in a wide variety of foods, people seldom lack of most of them.

“lack” is both a noun and a verb.

In this sentence we need a main verb and modified by the adverb ‘seldom’: lack something (v) (without preposition)

lack (n) often comes with the preposition ‘of’: lack of something ≈ shortage of something (n)

Because vitamins are contained in many foods, people rarely lack them.

⇨ Answer D. lack of => lack