The time and effort he has devoted during the past few years________ trees in that remote area is now considered to be of great value.
_____, he suddenly found the shop he was looking for.
I found John _____ the desk, _____ his homework carefully.
We must set about _____ our lesson for the mid-term examination.
I can't understand _____ at that poor child.
–Can you spare me some time? –I'm afraid not. I have lots of letters _____.