Pavement is most slippery in a rainstorm...?

Answer: C — Just after the storm starts

During a rainstorm, the water mixes with oil and other substances on the pavement, creating a layer of water that can make the surface slippery. Just after a storm starts, rainwater has not yet had a chance to wash away these substances, making the pavement especially slippery. As the storm continues, the rain will start to wash away the oil and other substances, reducing the level of slipperiness. Therefore, the pavement is most slippery just after a rainstorm starts. Option A is incorrect because just before the storm ends, the rain will have already washed away most of the substances on the pavement, reducing the slipperiness. Option B is incorrect because while the pavement is generally slippery throughout the entire storm, it is most slippery just after the storm starts. Option D is incorrect because by midway through the storm, the rain will have already washed away a significant amount of the substances