The correct option is C There is no meaning in what you say.
A Complex Sentence consists of one principal clause and any number of subordinate clauses.
A Noun Clause is a subordinate clause which does the work of a noun in a complex sentence.
In this case,
Option D is correct. The subordinate clause what you say acts as the object of the preposition in, in the principal clause. The object is always either a noun or a pronoun and as the subordinate clause in this sentence behaves as a noun, it is considered as a subordinate noun clause.
Option A is incorrect as an adverb clause has been used to combine the two sentences.
Option B is incorrect because it is a simple sentence.
Option C is incorrect as the subordinate clause behaves as an adjective clause.