A budget to cover paints and other supplies ________for the project will be pr
ovided by the city.
A. essential
B. essentially
C. more essentially
D. essentials
我选d 原因是我解读为用品，所以选名词。但答案是a 怎么解释呢？烦请高手协助谢谢

A budget ~ (which is) essential for ~