问题

Can you tell me _____ the birdwatchers in Zhalong Nature Reserve? I only know that _____ of them are from our school.
A:the number of; one- thirds
B:a number of; one-third
C:the number of; one-third
D:a number of; two-third
B:a number of; one-third
C:the number of; one-third
D:a number of; two-third
正确答案是: