27. I failed ________ why we had to wait in line for 1 hour only to ask a simple question. (A) to understand (B) in understanding (C) understanding (D) understood

31. Why did the researchers say eggs came after the chicken? (A) Because one of the egg-forming ingredients comes only from the chicken. (B) Because eggshell could be used to make a lot of products. (C) Because eggs are much lighter than the chicken. (D) Because they are British researchers.