✅ The clause 'Even though the economic forecast seemed bleak' begins with the subordinating conjunction 'even though', which signals a concession or contrast. This entire clause functions adverbially, providing context or a condition for the action/state described in the main independent clause ('investors remained cautiously optimistic').

❌ Option A is incorrect because 'even though' is a subordinating conjunction, not a coordinating conjunction. It introduces a dependent clause, not links two independent clauses of equal grammatical weight.

❌ Option B is incorrect because a nominal (or noun) clause functions as a noun (subject, object, complement), which is not the role of 'Even though the economic forecast seemed bleak' in this sentence. It does not name a person, place, thing, or idea that the verb acts upon.

❌ Option D is incorrect because a relative (or adjective) clause modifies a noun or pronoun, typically introduced by a relative pronoun like 'who,' 'which,' or 'that.' The clause in question modifies the entire action of the main clause, not a specific noun.