Choose the option which best replaces the underlined phrase.

"Happy is the man who acquired the habit of reading when he is young."

The option which best replaces the underlined phrase "who acquired" in the sentence "Happy is the man who acquired the habit of reading when he is young" is who acquires.

The sentence uses present tense "Happy is" and "he is young," so we need consistency in the verb tense. The relative clause should also be in the present tense to match.

Since:

• "Happy is" → Present tense
  • "man" → Singular noun

We need a present-tense, singular verb form after "who." The correct form is "acquires" (option 1), not "acquire" (option 3) which would be used with plural subjects.

Options 2 and 4 use past progressive ("was acquiring") and present perfect ("has been acquired") tenses, which don't match the simple present tense used in the rest of the sentence.

Hence, the correct answer is Option 1.