Final answer:
The given sentence is classified as a compound sentence (option c) because it contains two independent clauses joined by the coordinating conjunction 'but'. It does not contain dependent clauses, thus excluding it from being complex or compound-complex.
Step-by-step explanation:
The sentence "Semester exams will be in two weeks, but we still need to register for the second semester now." is an example of a compound sentence. This is because it consists of two independent clauses that can each stand alone as separate sentences. These clauses are joined together with the coordinating conjunction, which serves as a linker to combine the two main ideas into one cohesive statement.
In contrast, a complex sentence would contain an independent clause and one or more dependent or subordinate clauses. A simple sentence contains only one independent clause. Lastly, a compound-complex sentence is made up of multiple independent clauses and at least one dependent clause. The provided sentence does not have any dependent clauses; therefore, it does not fit the definition of a complex or compound-complex sentence.