16. You _____ return the book now. You can keep it till next week if you like.
The young couple was worried,because neither of them was aware ______ they had lost the necklace.
—At last I’ve made it.I am on top of the world.—______
We congratulated him ______ his getting a gold medal.That is to say: we offered him our congratulations ______ his getting a gold medal.
You have made a few mistakes in your composition but ______ you have done well.
In the experiment you should keep a watchful eye ______ the developments and record every detail.