key link的用法和樣例：
例句
- The classroom instruction is the teaching profession center link.
課堂教學是教學工作的中心環節。 - "A science fiction cannot not be regarded as a mere entertainment, but in fact it tells the reader much more."
"科幻小說不能簡單地看成是供消遣的，而實際上它給讀者展示更深刻的內容。" - Iron and steel industry is the key link in a nation's economy.
鋼鐵工業是一個國家經濟的主要環節。
