Categorize this sentence as belonging to either declarative, interrogative, imperative, exclamatory, or optative:
For how long will the sale last?
Interrogative.
Complete the following task based on the instruction and optional input provided.### Instruction:
Categorize this sentence as belonging to either declarative, interrogative, imperative, exclamatory, or optative:
For how long will the sale last?

### Output:
Interrogative.