6. Pyramids are really ______. It is hard to imagine how ancient Egyptians used primitive tools to build such magnificent structures. (A) aggressive (B) incredible (C) balanced (D) organic

10. The dirty air, known as smog, is a combination of weather conditions, fumes and smoke from cars and factories and therefore is sure to ______ many serious health problems. (A) bring up (B) give rise to (C) look forward to (D) have little to do with