Complete the sentence with a suitable verb:
I left my bike outside the house last night but this morning it wasn't there anymore.
Somebody______ it.
A. will have stolen
B. can have stolen
C. must have stolen
D. could have stolen

Hint: The modal verbs in the English language are auxiliary verbs used to express modality properties such as possibility, obligation, etc. The major English modal verbs to describe a possibility or surety of any action are can, could, may, might, must, shall, should, will and would, etc.

Complete answer:
'Will' specifies promise or voluntary action.
'Must' specifies compulsion or surety.
'Could' specifies ability in the past or possibility.
'Can' specifies ability or capacity or permission.
In the above sentence, the subject ‘I’ is sure that his bike has been stolen as he says in the sentence that he left his bike outside the house last night but this morning it wasn't there anymore. This sentence implies that the bike has been stolen surely. As no other reasonable expression explains the disappearance of the bike. But the subject ‘I’ is not sure that who the culprit is but he s sure about the bike being stole.
Here, the bike being stolen is not a promise or a voluntary, an ability in the past or a possibility, or ability or capacity or permission. It is compulsion or surety. So ‘must have stolen’ is the only appropriate option that can be used in the above sentence. Therefore, the correct answer is option C.

Note:
Verbs like "must-have", "can't have" and "might have" are used similarly as the present perfect. The action being described happened, or did not happen, in the past and is still true in the present. If "must-have" is used, it is believed that the action definitely happened.