(note that it's MP, we're unfavorable)
The auction starts:
1♦ - pass - 3♦ - ???
(opps play a very standard system, so opener shows 4+♦, and responder should show 10-11hcp and 4+♦)
You don't have any agreements about 4♣ being a 2-suiter, so it's natural for sure. What do you bid? And what's your plan later on?

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