Jane _____ these families of chimps for many years and helped people understand how much they behave like humans.
Since your English is poor, why not ________ an English club to improve it?
I think that's unlikely to happen, but if that_______, both America's and China's interest would be severely damaged.
One _____ of being able to speak English is that you will have more job opportunities.
---He lost his job last week, but he seems happy.---I think he _____ to put on a brave face.
The sick salesman was happy to stay at home because doing _____ was a thorough rest for him.