There are lots of different substances but only just over a hundred elements. An element is a substance that is made up of only one kind of atom. The atoms in a particular element are the same as each ...
In everyday life, for example on food packaging, the word ‘pure’ usually means that something is in its natural state without anything added to it, like sweeteners or preservatives. Natural fruit ...
当前正在显示可能无法访问的结果。
隐藏无法访问的结果