"Although our servers are stable,the telephone system is a serious concern" is a

A) simple sentence.
B) compound sentence.
C) complex sentence.
D) compound-complex sentence.

Complex Sentence

Sentence that expresses one main thought (the independent clause) and one or more subordinate, related thoughts (dependent clauses that cannot stand alone as valid sentences).

Servers

Servers are computer systems or software that provide data, resources, or services to other computers, known as clients, over a network.

Telephone System

A comprehensive network of electronic devices designed to connect calls between users over distances, utilizing wires or wireless signals.