Final answer:
The sentence "Don't forget to brush your teeth and comb your hair." is classified as a simple sentence due to its single clause with a compound verb structure. The implicit subject is 'you' in the imperative form.
Step-by-step explanation:
The sentence "Don't forget to brush your teeth and comb your hair." is an example of a simple sentence. Despite having two imperative verbs ('brush' and 'comb'), the sentence contains only one independent clause without any dependent clauses. In English grammar, a simple sentence is characterized by a single clause with a subject and a predicate, which can still include compound elements such as multiple verbs or objects. In this case, 'you' is the implicit subject (understood in the imperative form), and the verbs 'brush' and 'comb' are part of the same single clause with a compound verb structure. Therefore, the correct answer is (a) Simple.