adverb的擺位

兩個都對...adverb的位置由原始的文法規則到今天其實已經多從意義的表達邏輯上攞放多於固定規則位置作為標準

例如你提的例子其實沒有英語人會寫/講
They have still responded to our proposal.
因為你寫/講的要合理才成，have still repsoned是甚麼意思？他們己經仍在回答...?
adverb也要跟句中的verb能make sense才成句的
They have yet to response to our propsal.
或
They have still pending to reponse to our proposal.
才會合理

反語時把adv放在not前是常規。
除了
They still have not responded...
把adv放在句尾是較常見仍合理的
They have not responded...yet.
I don't know yet. (I yet don't know.會是很古老的英語文法)