Key__(solve) the problem is to meet thr damand__ (make)by the customers.

Key__(solve) the problem is to meet thr damand__ (make)by the customers.

to solving made
to 是介词+doing 翻译成.的关键
made 是后置定语 非谓语动词表示被动关系 被消费者提出的要求
The demand is made by the customers.= the customers make the demand.

to solve made