Quotes about Clean animals

Then Noah built an altar to the LORD. And taking from every kind of clean animal and clean bird, he offered burnt offerings on the altar.

Those that entered the ark in pairs were for the purpose of repopulating their kind after the Flood. This is why the female is paired with it. But the sacrificial clean animals were obviously not required to go in pairs as they had no mates and their function was not to keep their kinds alive after the Flood (Genesis 7:36). Sacrifice costs the sacrificer something. If not, it really isn't a sacrifice. King David later recognized this (2 Samuel 24:24