pp grammer test1 no 24...why??

pegirl

-----by the United States government's Bureau of Labor Statistics,the Consumer Price Index compares corrent costs of goods and services with past costs.


(A) To prepare


(B) As it prepared


(C) When preparation


(D) Prepared


Why answer is D???

shiran

从句的省略结构，被动语态。

enjoylife517

分词省略结构做状语。B,C结构不完整，A也应该用被动语态

pegirl

謝謝.....