A simple sentence connect by a subordinating conjunction to a compound sentence is know as

a compound-complex sentence.

A relative clause
a.begins with a coordinating conjunction such as and but,or,nor,and so on.
b.begins with a relative pronoun such as that,which,who,or whom.
c.has a subject and a verb and is a complete that can stand alone.
d. both b and c
I am not sure if it a

Your first answer is correct.

Your second answer is incorrect.
http://www.chompchomp.com/terms/relativeclause.htm

D is incorrect because C is incorrect.

Only B is correct for the second question.

Relative clauses are DEPENDENT clauses and can never be independent sentences on their own.

The correct answer is option d, "both b and c." A relative clause is a type of dependent clause that begins with a relative pronoun (such as that, which, who, or whom) and has a subject and a verb. It adds additional information to a sentence and cannot stand alone as a complete sentence. Relative clauses are often used to provide more details about a noun or pronoun in the main clause of a sentence. So, a relative clause can begin with a relative pronoun and is a complete clause that can stand alone.