They laughed a lot last night; The film ____________ very funny.

• অতীতে কোন কাজ বা ঘটনা নিশ্চিতভাবে ঘটেছিলো এরূপ অর্থ প্রকাশে must have + verb in past participle form ব্যবহৃত হয়।
- তাই শূন্যস্থানে সঠিক উত্তর হবে - must have been.
- Complete sentence: - They laughed a lot last night; The film must have been very funny.
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• Must have
- We use must have + past participle when we feel sure about what happened.

Example:
- Who told the newspapers about the prime minister's plans? It must have been someone close to him.
- The thief must have had a key. The door was locked and nothing was broken.
- Oh, good! We've got milk. Mo must have bought some yesterday.
- The streets are wet; It must have rained last night.

• Might have / may have
- We can use might have or may have + past participle when we think it's possible that something happened.

Example:
- I think I might have left the air conditioning on. Please can you check?
- Police think the suspect may have left the country using a fake passport.

Source: British Council