Choose the option that best represents the same sentence with the voice…

Concept: Exam grammar recognizes a set of "special passive constructions" that use idiom-like verb phrases instead of a literal "be + past participle" passive -- for example "This is beyond my power/control." Sentences built with "beyond + possessive + understanding/comprehension" belong to this recognized set and are converted to active voice by the fixed rule: "[clause] was beyond X's understanding" becomes "No one/Nobody understood [clause]." The universal negative already implied by "beyond anyone's understanding" surfaces as the explicit subject "No one", and "understanding" becomes the finite verb "understood".

Application: Here the clause "How he passed the exam so easily" is the fixed subordinate clause that must carry over unchanged as the object of the new sentence. The phrase "was beyond anyone's understanding" converts to "No one understood". Combining the two gives: "No one understood how he passed the exam so easily" -- exactly the transformation the rule predicts.

Checking the other options confirms none of them perform a genuine voice conversion:

• "Anyone understood how he passed the exam so easily" reverses the meaning: dropping the negation built into "beyond ... understanding" turns a statement of universal non-understanding into its opposite, an assertion that someone did understand.

• "It was beyond anyone's understanding how he passed the exam so easily" only reorders the clause after a dummy "It" subject; the idiom "beyond anyone's understanding" is untouched, so no voice change has actually taken place.

• "Beyond anyone's understanding, he passed the exam so easily" fronts the same idiom as an introductory phrase but again leaves "beyond anyone's understanding" intact, so this too fails to perform the required active-voice conversion.

Only "No one understood how he passed the exam so easily" genuinely converts the idiom into active voice, so it is the correct choice.