—What _______ the number of the students in your school? —About two thousand. A number of them _______ from the countryside. A. is; ,are B. is; is C. are; is D. are; are 答案:A生物的多样性包括( )A.生物种类的多样性、基因的多样性、生态系统的多样性B.植物的多样性、动物的多样性、微生物的多样性C.草原的多样性、森林的多样性、湿地的多样性D.生物因素和非生物因素的多样性