The companies are working together to create they hope will be the best means of transport in the 21st century.
The book didn’t _______ children probably because it employed too many scientific terms.
Speaking of all the songs he has written, I think this is probably his _______ one.
I would appreciate it _______ you call back this afternoon for the doctor’s appointment.
We can never expect _______ bluer sky unless we create _______ less polluted world.
We all know that, _______, the situation will get worse.