Tones can change when the same tones follow each other. There are rules for this, but really no need to try to wrap your brain around that yet. Just get real familiar with the correct tones first. You'll thank yourself later.
If there is a different tone and the word is spelled the same. They mean different things, different words
Do i really need to guess the meaning of these characters? Where in the lesson am i supposed to see what they mean? It feels like im missing something.
It's not particularly challenging when 元 only appears in the single option containing two characters...