She was engrossed in her book but happened to see that the man sitting beside her,
她全神贯注地读着书，忽然看见坐在她旁边的一个男子
看书为什么用被动was engrossed ？
忽然不是suddenly 可以替换but 吗变成suddenly，happened to see that the man sitting beside her,是吗
engross: to hold the complete interest or attention of (someone) —usually used as (be/get) engrossed.I dont think 忽然 is the correct translation here. It should be 但碰巧看见坐在她旁边的一个男子.
