What is the motivation behind this sudden change?
這種突然轉變背后的動機是什么？
The sudden noise made her start.
突如其來的聲音嚇了她一跳。
His heart gave a sudden leap when he saw her.
他看見她時，心猛地一跳。
The children were surprised by the sudden entry of their teacher.
老師突然進來使孩子們感到意外。