Many a time ________ swimming alone.
China has launched another man-made satellite,________ is announced in today's newspaper.
______ can do a job patiently and attentively for many years unless he loves it.
Environment protection requires our joint effort. ______ will be achieved unless we work well together.
---Can I join your club, dad?---You can when you _______ a bit older.
Because the shop_______, all the T-shirts are sold at half price.