The correct option is A whom we saw on national television
An adjective clause is a group of words that contain a subject and a
verb, and it functions as an adjective that modifies a noun or a
pronoun. Adjective clauses usually begin with relative pronouns such as
who, whom, whose or a relative adverb like when, where and so on.
Option A is correct as it begins with the relative pronoun "whom", has a subject "we" and a verb "saw".
Option B is incorrect because it is a phrase, not a clause.
Option C is incorrect because it is an adverb clause of time; "while" is an adverb of time.
Option D is incorrect because the answer lies in A.