The correct option is A that is lying on the sofa
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 is an adjective clause containing a subject 'that'
(which is a relative pronoun), a verb 'is lying' and modifies the noun
"bag".
Option B is incorrect because it is a phrase, not a clause, it does not have a subject nor verb.
Option C is incorrect because this is also a phrase.
Option D is incorrect because the answer lies in A.