He was a friendly man most of the time, but he could become nasty.
He could be really friendly, or he could be miserable.
It was a warn day, yet the storm clouds gathered over the distant mountains.
It was a beautiful morning for a walk, so he set off quite happily.
A BOYS sentence has two parts. The first start ends with a comma, and the second part starts with one of the words: but, or, yet, so.
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