Final answer:
You should be most careful when driving during the first half hour of rain due to oils on the road surface creating slippery conditions.
Step-by-step explanation:
When it is raining, you should be most careful when turning or stopping during the first half hour of rain. This is because the rain causes oils and gasoline that have leaked onto the road surface to rise, creating a slippery layer. In contrast, a heavy rain can wash away the oil, improving grip, but excessive water can lead to hydroplaning. Always adjust your driving according to the conditions to maintain control of the car. Remember that road safety during adverse weather conditions is crucial, so exercise additional caution and reduce your speed appropriately.