"Keep carrots away from apples, or the carrots will turn bitter. "

Actually apples will do all sorts of things to other fruit/veges stored near them - they give off acetylene - a gas that used to a banana ripening agent. Put one in a brown paper bag with many things, bananas, pineapples avocados - all sorts of things, just try it - and it speeds up the ripening process.

Apples are best kept away from many things, but then other stuff may give it off too.

Hmmm An apple a day keeps the doctor away - if you don't have apples, but a welding cylinder....