B. Yogurt is a kind of dairy product, which takes fresh milk as raw material, adds beneficial bacteria (starter) to the milk after pasteurization, cools and fills after fermentation. Correct;
C. Clenbuterol is a hormone and is not easy to decompose. Long-term use is harmful to human health, so it is wrong;
D, gutter oil can be reused, but it contains many metamorphic ingredients, which is harmful to human health, so it is wrong;
So choose B.