The family is a cooperative enterprise for which it is difficult to rules, because each family needs to work out its own ways to deal with its own problems.
A. set up
B. put down
C. keep up
D. lay down
网友回答
A. set up
B. put down
C. keep up
(答案→)D. lay down
解析： lay down制定符合句意；A建立，创立；C保持。