House owners keep their gardens in a neat and orderly state according to the regulations.A

问题补充：

House owners keep their gardens in a neat and orderly state according to the regulations.

A. may

B. would

C. can

D. shall

答案：

A. may

B. would

C. can

(答案→)D. shall

解析：句意：根据条例，房子的主人必须保持他们的花园整洁有序。shall用于法律，条款中表示必须要遵循的准则和条例，故选D