(it's) no/little/small wonder
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难怪我们今天一片混乱。
It's little wonder we are in a big mess today.
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难怪他有点儿不高兴。
No wonder he was a bit upset.
pardonable; understandable
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他很害怕,这也难怪,毕竟还小嘛。
It's understandable that he was frightened; after all, he is only a child.