______life began on the earth is one of the biggest puzzles to scientists.
I thought you ____ like something to read , so I have brought you some books .
I can''t find Jane anywhere in the office building . Where ____ she have gone ?
Mary ____ be in Paris . I saw her a few minutes ago .
You are wet through . You ____ in the rain .
Put on more clothes . You ____ be feeling cold with only a shirt on .