Final answer:
The statement provided in the question is false because the sentence given is a compound sentence, not a compound-complex sentence; it lacks a subordinate clause which is required for a compound-complex sentence structure.
Step-by-step explanation:
The statement 'Sally went trick-or-treating as a cat but dropped her mask while picking up candy, creating a compound-complex sentence.' is false because the sentence provided is not a compound-complex sentence. A compound-complex sentence is one that has at least two independent clauses and at least one dependent clause. The sentence given has two clauses, but they are coordinated by the conjunction 'but,' making it a compound sentence, not compound-complex. To be a compound-complex sentence, there must be another clause that is subordinate to one of the main clauses, such as '...as a cat, but she dropped her mask while picking up candy, which made her sad.'