Translation:I am sick. I can't attend your party.
It doesn't matter; in English unless you're playing D+D you don't "join" a party. So in that context it very definitely means "come to"/"go to" which are interchangeable in this context.
These sentences united by a comma are a nightmare. Sometimes the translation is a dot, sometimes "and". Why not accept both?
Just suggest any correct missing answer then they will accept both. This is what this beta course if for after all.
We don't say "attend" a party. A much more natural translation is "I can't come to your party."
'Sick' and 'ill' should both be accepted. Only the millionth time I have had to report this, as DL only corrects individual sentences without making identical corrections elsewhere on their sentence database.
How would you say, "I was sick"? I was thinking this sentence was in the past tense because of the "le" but I realize it can also be used to describe a condition that is temporary, ie: i won't always be sick, but I am sick now.
The 了 here signifies a change of state. The implication is that I was not sick when you invited me, but I've gotten sick in the meantime.
参加 is most commonly associated with "joining" or "attending" , and in this case those two are 100% okay. A more casual phrase in Chinese could warrant a more casual translation like "come to" or "go to" your party.
Isn't 我生病了more like "I (just) got sick"? I feel like that would be a good way to translate the 了 in this case
"I am sick and can't attend your party." should be considered correct.