幾個文法觀念（最高級同位語關代） - 足球

1. Our company has always sought the most ___ qualified and skilled practitioners in the field of management.
為什麼是highest? 而不是highly??
qualified跟skilled應該用highly來修飾吧？？
2. You ____ his offer in the first place. It's almost impossible to find a client as good as him.
為什麼是shouldn't have turned town而不是couldn't turn down?
因為could應該改成can嗎？ 兩個差別在過去式？？
should後面應該接過去式才對吧？為何接完成式呢？
3. William, _____ at the Kaohsiung book sighing, said that the book launch was a "bittersweet" day for him, since his father didn't live to see it.
為什麼是who spoke不是spoke？
不是用PP形成同位語不是嗎？
如果是who spoke的話逗點不加可以嗎？
4. Many people recognize basketball as their favorite sport, but few know of its origin. _____, the game's popularity is more than 100 years old.
為什麼用In fact不能用For example?
很多人喜歡籃球卻不知到期起源 例如 他是在100年前普及
這樣也蠻順的阿@@
5. The ball _____ was a soccer ball.
為什麼用used不能用to use?
前後文這句意思應該是一開始是用足球來打籃球
這邊used是什麼文法 沒有看過可以這樣用耶？ 他是動詞嗎？
這幾個觀念不太懂
謝謝！！