1. - Look! What a mistake! Why? - Sorry, I _ on it. A.dont concentrate B. hadnt concentrated C. hadnt been concentrating D. wasnt concentrating 2. There are so many beautiful things that it was hard _. to choose B. to be chosen C. choosing one D. to choose from 3. With his money _ and his health ruined, he couldnt go home. leaving B. missed C. running out D. run out 4. _ is known to us all is that the old scientist, for _ life was hard in the past, still works very hard in his eighties. A. As, w
