16. The roads might have been slippery __ unless you were out driving long distances (B)) so you ought to drive carefully C) as long as the tyres of the car were in good shape D) if it had been pouring with rain for two days E)supposing that you had bad car tyres

The correct answer is D) if it had been pouring with rain for two days.<br /><br />The sentence "The roads might have been slippery" suggests that the roads could have been slippery under certain conditions. Option D) "if it had been pouring with rain for two days" provides a plausible condition that could have caused the roads to be slippery. Continuous rainfall for an extended period can lead to the accumulation of water on the roads, making them slippery. Therefore, option D) is the most appropriate answer.