There are many people there; something __________.

- উল্লেখিত প্রশ্নের সঠিক উত্তর হচ্ছে must have happened.

• কোনো কাজ ঘটেছে (present perfect tense এর ভাব) এরূপ অনুমান বুঝালে may/ might have + verb in past participle.
Example:
There are many people there; something must have happened.
The street is wet; it must have rained.

Source: A Passage to the English Language, S.M. Zakir Hussain.