The sentence "These past few days have been extremely hot." is a **simple** sentence.
Here's why:
1. **Structure**: A simple sentence contains one independent clause, which is a complete thought with a subject and a predicate. In this sentence, "These past few days have been extremely hot." forms a complete thought with the subject "These past few days" and the predicate "have been extremely hot."
2. **Complexity**: There are no dependent clauses or additional phrases in the sentence. It is straightforward and does not contain any additional clauses that would make it compound, complex, or compound-complex.
Therefore, the sentence "These past few days have been extremely hot." is a simple sentence.
