单选题 If x and y are positive integers, what is the value of y?(1)21x+20y=500(2)x+y=24

A、 Statement (1) ALONE is sufficient, but statement (5) alone is not sufficient to answer the question asked.
B、 Statement (2) ALONE is sufficient, but statement (4) alone is not sufficient to answer the question asked.
C、 BOTH statement (1) and (5) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient.
D、 EACH statement ALONE is sufficient to answer the question asked.
E、 Statement (1) and(5)TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.

【正确答案】 A

【答案解析】x，y都是正整数。单独(1)得到y=25-21x/20，由于20和21互质，那么x必然是20的倍数，但是由于y也是正整数，所以必然取20，这样，y的值也就确定，所以A为正确答案。