Which of the following is a complex sentence?

Question

Although the dentist found nothing wrong with Sue's teeth, she still had a toothache, so she went to bed.

The dentist did not find anything wrong with Sue's teeth.

The dentist did not find anything wrong with her teeth, but Sue continues to have a toothache.

Although the dentist did not find anything wrong, Sue's mouth still hurt.

Answer 1

Although the dentist found nothing wrong with Sue's teeth, she still had a toothache, so she went to bed.