求助一个很弱的问题

212. The Baldrick Manufacturing Company has for

several years followed a policy aimed at decreasing operating costs and improving the efficiency of its distribution system.

(A)  aimed at decreasing operating costs and improving

(B)  aimed at the decreasing of operating costs and to improve

(C)  aiming at the decreasing of operating costs and improving

(D)  the aim of which is the decreasing of operating costs and improving

(E)   with the aim to decrease operating costs and to improve

此题答案是A, 为什么答案用aimed 而不是aiming? 先谢了!

be aimed at 固定用法