The correct option is B Complex Sentence
A complex sentence is made up of two or more clauses, where at least one
of them should be independent, i.e., complete in meaning. The other
clause/clauses should be dependent; it should depend on the
main/independent clause for its complete meaning. The given sentence is made up of a dependent clause "Although the kid is new in school" that depends on the main clause "she has managed to make a lot of friends today" for its full meaning. Hence, the sentence is complex and option C is correct. A simple sentence contains only one clause. A compound sentence requires both independent clauses, hence options A and B are incorrect. Option D is incorrect because the correct answer lies in C.