I don't feel very well. - Here, 'well' is - adjective.

- এখানে ‘well’ হলো adjective, কারণ এটা ‘feel’ verb এর সঙ্গে ব্যবহার হয়ে স্বাস্থ্য বা অবস্থা (health condition) বর্ণনা করছে।
অর্থাৎ ‘I am not healthy/comfortable’ এর অর্থে।

• Well: [adjective]
English meaning: in good health
Bangla meaning: সুস্থ

Example:
- I don't feel very well.
- Is she well enough to travel?

Options,
ক) The dog fell down a well.
- এখানে ‘well’ হলো noun, অর্থাৎ কুয়া বা গর্ত।

• Well: [noun]
English meaning:
- a deep hole in the ground from which people obtain water. The sides of wells are usually covered with brick or stone and there is usually a cover or a small wall at the top of the well.
Bangla meaning: কূপ; কুয়া।

Example:
- The dog fell down a well.

খ) Well, well—I would never have guessed it!
- এখানে well হলো interjection (হতবাক্য/হঠাৎ অভিব্যক্তি) যা বিস্ময় বা আশ্চর্য প্রকাশ করছে।

• Well: [Interjection]
Meaning: used to express surprise, anger or relief.

Example:
Well, well—I would never have guessed it!
Well, really! What a thing to say!
Well, thank goodness that's over!

ঘ) The kids all behaved well.
- এখানে well হলো adverb, কারণ এটি “behaved” (verb) কে describe করছে।

• Well: [adverb]
English meaning: in a good, right or acceptable way.
Bangla meaning: ভালোভাবে; সঠিক বা সন্তোষজনকভাবে

Example:
- They played well in the tournament.
- The team work well together.
- The kids all behaved well.
- The conference was very well organized.

Source: Oxford Dictionary.