"Is the wind weak?"
Yep, once again penalized for using Kanji. It's virtually impossible at the moment to guess what they want spelled out in hiragana and what they want in Kanji.
I input 風は弱いですか ( both with and without question mark) and got marked wrong. Most of the time, inputting kanji, or leaving out punctuation is accepted, but seemingly not here.
it always depends on the context, but one of the possible reasons is when you use “は”, you want the listeners to pay attention to the part after “は”. But when you use “が”, it turns to the part before “が”, to emphasize it.
よわくis the adverb, よわい is the adjective. Think of it as "Weakly"(adverb) vs "Weak(adjective).