You should take regular exercise. (Imperative)

The correct answer is - খ) Take regular exercise.

• Affirmative থেকে Imperative করার নিয়ম -
- Imperative করার ক্ষেত্রে Affirmative Sentence এর মূল verb এর present form + প্রদত্ত verb এর পরের অংশ হবে।

Affirmative: You should do the work.
Imperative: Do the work.

Affirmative: You speak the truth.
Imperative: Speak the truth.

Affirmative: You read the book.
Imperative: Please, read the book.
or. Read the book, please.

Source: Advanced Learner's English Grammar & Composition by Chowdhury & Hossain.