______ the ancient Egyptians built the pyramids puzzled people for centuries.
Michael Jordan, known as ____ top scorer in _____ NBA, did much charity work for society.
---I hear Johnson was badly injured in the accident. ---_____, let's go and see him.
Some researchers believe that there is no doubt ____ a cure for AIDS will be found.
Don't panic; just ______ the rock and I'll come and fetch you down.
With a lot of difficult problems ____, the newly -elected president is having a hard time.