By ________ nature, you are an adventurer, full of amazement and curiosity about _________world bigger than life itself.
Green is usually regarded as a __________ of life while red stands for joy and victory. A. symbol B. sign C, mark D. signal
It's rude __________ you to ask his salary the first time you __________ him.
We should consider the students' request __________ the school library provide more books on popular science.
—How much do you know about the 3D film technology?_ A little. Not until the hot movie Avatar __________ some about it.
Some of you may have finished unit one. __________ you can go on to unit two.