问题
31. －A number of volunteers ____ willing to work in 2016 Rio Olympic Games this year.－Yes, it’s reported that the number is getting ____.
A:is; bigger and bigger
B:are; bigger and bigger
C:is; more and more
D:are; more and more;
B:are; bigger and bigger
C:is; more and more
D:are; more and more;
正确答案是：
