the key to solving problem 的to 为什么是介词?

the key to solving problem 的to 为什么是介词? The key to solving the problem . The key to solving the problem the key to solving the problem is to meeet the demand made b We are looking forward to solving the problem这句话的翻译 Have you got the key to teh problem?=Have you the problem?是空 Do you know the key to the problem?为什么用to不用for the key to solve the problem is to _____ trees I have never given ___ solving the problem.[应该是填in to 还是up,还 3． Many ways can contribute to solving this problem,but the The key ___the problem is to meet the demand___by customers 英语翻译门的钥匙翻译为什么是 a key to the door 可不可以是a key of the door呢~