What must you reckon with when it starts raining after a long period of dry weather?

You answered correctly. When it starts raining after a long dry period, oil, dust, and dirt that have accumulated on the road mix with the water, creating a slippery, greasy film. This makes the road particularly hazardous and increases the risk of skidding. Additionally, when you first switch on the windscreen wipers, dirt and dust on the windshield can smear, temporarily reducing your visibility. The braking distance will actually become longer, not shorter, due to the reduced grip. Always drive more cautiously in these conditions and be prepared for slippery surfaces and limited visibility.