B. Vitamins are relatively stable in low temperature and acidic solution, and eating cucumber mixed with vinegar is better for taking vitamins, so B is correct;
For example, a large number of disposable plastics are easy to cause white pollution, so it is wrong;
D, the oil pan accidentally caught fire, you should use the pot cover to put out or pour lettuce, you can't use a lot of water to put out, otherwise it will easily cause oil droplets to splash, so D is wrong;
So choose B.