Final answer:
Option D is an example of a complex sentence. It consists of two independent clauses connected by the conjunction 'and'.
Step-by-step explanation:
A complex sentence is a sentence that consists of an independent clause (a clause that can stand alone as a sentence) and at least one dependent clause (a clause that cannot stand alone as a sentence). In the given options, option D is an example of a complex sentence. It consists of two independent clauses: 'Animal testing is cruel' and 'it should be stopped immediately'. The conjunction 'and' connects the two independent clauses.