31. Lan said she would go to Ha Noi the next day. 

Grammar: reported speech 

will => would; tomorrow => the next day 

32. New devices have been invented by scientists to help people live a longer life.

Grammar: passive (O1 + BE + VED/3 + BY S + O2)

have invented => have been invented 

33. After having provided food, they cleared up the debris. 

provided (quá khứ) => having provided 

Sau AFTER + Ving

`31,` Lan said that she would go to Ha Noi the following day.

Câu gián tiếp dạng trần thuật:

`-` S `+` told/said `+` that `+` S `+` V(lùi thì)…

I -> she

will -> would

tomorrow -> the following day 

`32,` New devices have been invented to help people live a longer life by scientists.

`-` Câu bị động HTHT: S `+` have/has `+` been `+` V3/V-ed..(by `+` O) 

`33,` After they had provided food, they cleared up the debris.

`-` After + QKHT, QKĐ 

`+` Diễn tả sau khi 1 hành động kết thúc thì 1 hành động khác diễn ra.

`-` QKHT: S `+` had `+` V3/V-ed `+` O

`-` QKĐ: S `+` V2/V-ed `+` O

`->` Sau khi họ cung cấp nguồn thức ăn xong, họ đã dọn dẹp đống đổ nát.