I don't know if you noticed their behaviors or not, but we______.
This school was the first __________ textbooks as well as reading materials.
You can never be __________ when crossing the street.
—He was nearly drowned once. —When was __________? —__________ was in 1998 when he was in middle school.
1 could just see a car in the distance, but I couldn't __________ what colour it was.
After ten years' hard work, she finally __________ all the debts.