16. The computer program is a puzzle to me. The more I think of it, the more questions I think of _____.
The country has _______ great changes and become a developed one.
We are often _____ by the doctors to eat more healthy food and take plenty of physical exercise.
We asked the teacher to explain _______.
—Did you see a man in black pass by just now? —No, sir. I ______ a newspaper.
Only by working hard can you ______ the goal.