if A、B、C three node has same content，The current design strategy is to download from the nearest node, or at the same time from three nodes？thanks！！
If you are using a public network you can easily get the content automagically by:
ipfs get $HASH
This should get the content from all of them.
But, I suggest to connect directly to these nodes, and if you are using a private network, you need few extra step to ensure that the private key is there and configured correctly.