Although the dentist found nothing wrong with Sue's teeth, she still had a toothache, so she went to bed.- this is a complex sentence.
Option: D
Explanation:
In English language sentence is always made up of two clauses. One independent or principal clause and one dependent or subordinate clause. Independent clause means a sentence which can stand alone, no need of being with coordinating or subordinating clauses. For e.g. Sue's mouth still hurt.
Dependent clause means which sentence needs help of another sentence through conjunction to be meaningful. Like Although the dentist found nothing wrong with Sue's teeth, she still had a toothache, so she went to bed. In complex sentence there must be one dependent clause.
