Final answer:
Roads are most slippery at the beginning of a rainstorm following a dry spell, due to oil and gasoline residue on the road that make the surface slick when mixed with a light rain.
Step-by-step explanation:
Roads tend to be the most slippery during the beginning of a rainstorm, especially if it follows a long dry spell. This is because, as cars travel, oil and gasoline can leak onto the road surface. When a light rain starts after a dry period, it mixes with the oil residue creating a slippery film on the roadway, making it more dangerous for vehicles. Heavy rains, conversely, can wash away the oil and gas, reducing the slipperiness after the rain persists for some time.
Consequently, the correct answer to the question is: Roads are the most slippery B.The first rain after a dry spell.