The painting is the most expensive one _____ he bought.
Last year he had an opportunity ______ abroad, but he gave it up.
---Whose book is this? ---It ______ be Linda’s. It has her name on it.
There are ______ flowers in the square during the National Day.
---How do you learn English? ---I learn watching English videos.
---Did you get there by ______ bike?---No, I took ______ taxi.