"The wind blows weakly in summer."
"Ha" defines the subject of the phrase (the information you already know) "ga" means "is" . So after that, the info you want to comunicate will be something new, to know, or learn... Hope it helps you... English and japanese arent my native languajes
Couldn't we also say something like ”夏で風は弱く吹きます” (natsu de kaze wa yowaku fukimasu) or "風は夏に弱く吹きます" (kaze wa natsu ni yowaku fukimasu)?
Duolingo only ever really accepts one answer. Plus some of the kanji used hasn't been introduced to learners yet.
Yes. For i-adjectives replace the final い with く to form an adverb (same way as creating negative adjective phrases.