1. They spent two hours looking for your house
`=>` How much time did they spend looking for your house?
Giải thích: two hours là từ chỉ thời gian (về số lượng) `=>` How much time
2. They had an exam last week.
`=>` When did they have an exam?
Giải thích: last week là tử chỉ thời gian `=>` when