The word "vary" is closest in meaning to which of following?

　　(A) mean

　　(B) stretch

　　(C) change

　　(D) include

　　219. However, the amount of helium that could have been produced in this manner can be calculated, and it turns out to be no more than a few percent.

　　The word "calculated" is closest in meaning to which of following?

　　(A) ignored

　　(B) converted

　　(C) increased

　　(D) determined

　　220. By the time the universe was a few minutes old, helium production has effectively ceased.

　　The word "ceased" is closest in meaning to which of following?

　　(A) extended

　　(B) performed

　　(C) taken hold

　　(D) stopped