Students often write a single sentence that contains the conjunctions “although” and “but”. This is probably a bad idea. You should just pick one.
You can write:
“Although I studied hard, I couldn’t pass the test.”
And you can write:
“I studied hard, but I couldn’t pass the test.”
Can you see how each of those sentences has just one of the conjunctions?
Don’t write a sentence with both of them. You shouldn’t write:
“Although I studied hard, but I couldn’t pass the test.”
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I suppose this is the same as combining “because” and “so” in the same sentence, but that’s a topic for another post.