Final answer:
The sentence in question is a simple sentence because it has one main clause that conveys a complete idea, regardless of the additional information about the dentist appointment and soccer practice. Therefore, the correct answer is a) Simple.
Step-by-step explanation:
The sentence 'Don't forget that you have a dentist appointment and soccer practice.' is a simple sentence. This is because it contains one main clause, with a single subject (you) and a single predicate (don't forget), which conveys a single complete idea.
Although the sentence includes additional information that you have two activities to remember, the dentist appointment and soccer practice, they are part of that same single instruction and thus, do not create a separate main clause that would be necessary for a compound sentence.
The sentence 'Don't forget that you have a dentist appointment and soccer practice' is a simple sentence despite the use of 'and' because it contains only one main clause with a single subject and verb giving a directive.
The conjunction 'and' in this sentence connects two objects of the verb 'have', creating a list, but not connecting two independent clauses, which would classify it as a compound sentence.