Which sentence correctly uses an infinitive?

• Correct answer - You need not worry about the result.

• Infinitive:
- Verb এর present form এর আগে to বসিয়ে Infinitive গঠন করা হয়।
- অর্থাৎ, Infinitive = to + verb.

• Infinitive দুই রকম হতে পারে-
1. To-যুক্ত infinitive এবং
2. To-বিহীন infinitive বা Bare Infinitive.

• Bare Infinitive:
• নিম্নলিখিত verb-এর পরে infinitive (to) বসে না।
(a) can, do, may, must, shall, will এর পরেঃ
- I may help you.
- He must do it.

(b) need এবং dare - auxiliary verb হিসেবে ব্যবহৃত হলেঃ
- I dared not wake him.
- They need not do anything.

- কিন্তু ordinary verb হিসেবে ব্যবহৃত হলে তাদের পরে infinitive (to + verb) বসে।
- I did not/didn't dare to wake him.
- They do not/don't need to do anything.

(c) feel, hear, let, see, make, watch-এর পরেঃ
- I saw him go.
- The old man watched his companions fall down dead.

- কিন্তু Passive Voice-এ see, hear, এবং make এর পরে full infinitive ব্যবহৃত হয়।
- Active voice: I saw him go.
- Passive voice:He was seen to go.

(d) Had better, had rather, had sooner, would rather/would sooner, rather than/sooner than/ as soon as ইত্যাদির পরেঃ
- You had better start at once. (to start নয়)

(e) "Than" Conjunction-এর পরে to উহ্য থাকে।
- I would rather die than beg.

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