As far as I'm concerned, 'has to' and 'must' are the same damn thing. Grrr ...
So what the hell does it mean if 'aimer' is replaced with 'adore' in this sentence??? You'd think in the language of love, love would be represented clearly....
It is not for us to judge if the feeling is stronger or weaker between this boy and his dog than between this grandmother and her children. Translation exercises show you various feelings and you need to understand them before you translate them to the closest English verb, not the one you would like.
I hate this aimer business so much that I would prefer (in real life) to NEVER use this verb. I took 6 years of French in school and never had this hard a time about like vs love (and I am sure if it had been explained well then, I wouldn't be so confused now). That it doesn't seem to be consistent even within Duo doesn't make it any easier. THIS CONFUSION MAKES ME KIND OF HATE FRENCH. SO FRUSTRATING.
Relax. It's not that different from English. We say "I love spaghetti" and "I love my grandma." But we know that both are not the same kind of love. We really mean that we LIKE spaghetti and LOVE grandma.
It's the exact same thing in French: J'aime (like) les pâtes et j'aime (love) ma grand-mère. Just be careful when you translate them.