We work together to achieve our common purpose: _________ world that is safer, cleaner and healthier than __________ one we are living in.
—He plays basketball so well! Who taught _______? —He learnt it by _______.
—_______ can I keep the books? —Two weeks.
My mother often tells me _______ my classmates when they need.
Do you prefer _______?
You should _______ the doctor’s advice and _______ the medicine on time.