Chemistry. If you take an acid of 9 and add an acid of 7, the acid becomes the one inbetween. So the two merge together and become 8.

更多英語謎語

Is it legal for a man to marry his widow's sister?

Where does divorce come before marriage?

What do you have to lift the top up to put the bottom down?

What will you add to a barrel filled with milk to make it lighter?