1.School start at nine o'clock.改错并语法说明 2.He is a five-years-old boy.

1. School starts at nine o'clock. 主语书School 属于第三人称形式，所以要用 starts
2. He is a five-year-old boy. five-year-old 固定用法。
另注比较一下 He is five years old.

1. 应该是School starts at nine o'clock.因为学校是第三人称单数，所以start后加s
2 应是.He is a five-year-old boy. five-year-old 这是固定用法 还有 ten-year-old

start换成starts 因为主语school是单数，谓语动词也要保持一致用第三人称单数，故加s
five-years-old换成five-year-old 此类形容词year不加s

1..School will start at nine o'clock（时态有问题）
2.five-years-old 换成five-year-old

1.School starts at nine o'clock.School 是单数形式,后面的动词start要加s
2.He is a five-year-old boy.five-year-old 是个定语,year不需要加s