OG 239 题干看不懂

og 239. Organized in 1966 by the Fish and Wildlife Service, the Breeding Bird Survey uses annual roadside counts along established routes for monitoring of population changes of as many as, or of more than 250 bird species, including 180 songbirds.

(A) for monitoring of population changes of as many as, or of

(B) to monitor population changes of as many, or

(C) to monitor changes in the populations of

(D) that monitors population changes of

(E) that monitors changes in populations of as many as, or

请问annual roadside counts along established routes什么意思？

应该是　沿着已建路线设立的每年的路边计数器（计数器？）　　吧