I don't understand why "了" is used with being sick ("生病了") and having a cold ("感冒了"), but not having a fever ("發燒了").
Of course you can say 发烧了
Natives of English: can I say "he has fever" instead of "he has a fever"? I thought you could go either way, but this course enforces the indefinite article upon me…
It's "he has A fever". The only time the indefinite article isn't used that I know of is when it's in the name of a disease like "scarlet fever" etc.
Is 的 really required with 哥哥 (close relation)? Duo not accepting 我哥哥发烧