I guess the man with red hair may have caused it.

EASY answer

Knowledge of modal verbs

Topic: I guess the man with the red hair did this.

D. It may have been caused by the man with red hair

The remaining answers:

A. wrong because “his” is, because “whose” is already a possessive relative pronoun instead of the noun “the man”

B. is incorrect because the relative clause “whose red hair” is incomplete and lacks a verb; The verb “may have caused” behind is the main subject “the man” in front

C. is wrong because it needs to be conjugated in the passive voice for the subject “it”

Note: the structure “may have Vp2” to describe an action that is likely to happen in the past but is uncertain because there is no clear evidence or basis.