问答题 Complete these sentences with a suitable preposition.
1. Sales have risen ______ 10%.
2. Production has increased ______ 2,000 units to 2,500 units.
3. Sales usually increase ______ Christmas time.
4. I'm sure there will be a fall ______ interest rates.
5. Unemployment always increases ______ winter.
6. I think there will be a rise ______ 15% in production.