A complex sentece is a sentence which contains an independent clause and at least one dependent clause. So, the correct answer is letter D.
Explanation:
Independent clause: Animal test is cruel.
- Animal test: subject
- is: verb
Depedent clause: and it should be stopped imeddiately.
- Coordinate conjunction: and
- subject: it
- modal verb: should
- verb: be stopped
- adverb: immediately
