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
我選d 原因是我解讀為用品，所以選名詞。但答案是a 怎麼解釋呢？煩請高手協助謝謝

A budget ~ (which is) essential for ~