সঠিক উত্তর — ক) Put the book back on the shelf.

• এখানে back verb কে (put) modify করছে, অর্থাৎ "আগের জায়গায়" বা "ফিরিয়ে" দেওয়া বোঝাচ্ছে।

- এটি adverb.

Options,

খ) He was lying on his back on the sofa.
→ back এখানে noun (পিঠ)।

গ) We were sitting in the back row.
→ back এখানে adjective (row-এর অবস্থান বোঝাচ্ছে)।

ঘ) We drove along miles of twisty back roads.
→ back এখানে adjective (roads-এর ধরন বোঝাচ্ছে)।

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• Back: [adverb]
English meaning: to or into the place, condition, situation or activity where somebody/something was before.
Bangla meaning: আগের অবস্থান, অবস্থা বা কাজে ফিরে যাওয়া।

Example:
- When is he coming back to work?
- He'll be back on Monday.
- Don't forget to bring it back when you've finished with it.

Options,

• Back: [noun]
English meaning: the part of the human body that is on the opposite side to the chest, between the neck and the tops of the legs; the part of an animal’s body that corresponds to this.
Bangla meaning: (মানবদেহ সম্বন্ধে) পিঠ; পৃষ্ঠদেশ; মেরুদণ্ড।

Example:
- He was lying on his back on the sofa.

Back: [adjective]
English meaning: located behind or at the back of something.

Example:
- We were sitting in the back row.
- We drove along miles of twisty back roads (= away from the main roads).

Source: Oxford Dictionary.