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that's why

Choose between that's why, since, whereas:

David wasn't surprised when he was eliminated, he knew he was a bit behind.
He lived far from home, he sometimes missed his family.
The candidates have to keep fit, they have to exercise every day.
At the end the group cracked, they got on well at the beginning.
He didn't have any musical training, other contestants did.
I knew that girls supported me, most boys didn't.
All of the others had some musical training, I didn't have any at all and I felt I was a bit behind.
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