The most important thing about cotton in history is ___part that it played in ____Industrial Revolution.
—Did you ask your pen pal ___?—Yes, he’ll come here after the exam.
I found lots of people were visiting the beautiful mountains when I ___ the car.
I’d like to have a picnic with you in the park. ___ , I’m too busy today.
The doctor ___ the crying boy, but he couldn’t find what was wrong with him.
After walking for 4 hours, he was ___ tired ___ move on.