Susan started to clean the room; Lily was preparing lunch.
We went through a period _____ communications were very difficult in the rural areas.
I like getting up very early in summer. The morning air is so good ______.
On the north of the bank _____ the Opera House, _____ was built two hundred years ago.
One learns a language by making mistakes and ________them
________ on the top of the hill, you can enjoy a good view.