Complete the sentence with suitable alternatives from the options given below.

Sumit is obedient, someone else ________ done it.

must have

The correct option to complete the sentence is must have. The completed sentence is:

Sumit is obedient, someone else must have done it.

The verb must have indicates that the action was done in the past and there is a high degree of probability that it was done by someone other than Sumit.