"I hope that it's not a serious disease."
Translation:J'espère que ce n'est pas une maladie grave.
"j'espere qu'il n'est pas une maladie serieuse" - rejected. It could be because I used serieuse, not grave. I hesitated between the two, but the hover hints suggest serieuse, and not grave. So, that is what I used. Reported that in case I was dinged for that. Of course, it could be that I have to use 'ce' not 'il'. If so, is there a way to know if you should use 'ce' or 'il' as the translation for it? Is there a rule as such, or do you just have to know when to use one and when the other? Anyway, I have also reported that I think my answer should be accepted. I appreciate I may be wrong on this, but at least DL will take a look at this.
Generally speaking "il est un + noun" or "elle est une + noun" is a no-go. When "il est/elle est" is followed by a determiner + a noun, you have to use "c'est".
- He is a nice man = C'est un homme gentil
- She is a good citizen = C'est une bonne citoyenne
- It is a serious disease = C'est une maladie grave