1. ________ did Arthur realize that there was danger.
2. In mathematics, a variable is a symbol ________ some element of a set.
3. Few natural elements exist in ________ that they are rarely seen in their natural environments.
4. The janitor refused to unlock the classroom door because he ________ busy.
5. ________, which is the highest in the range, appears challenging.
6. The student managed to pass the entrance examination ________ he was blind.
7. John F.Kennedy was the youngest president of the United States and ________ to be assassinated.
8. ________ the formulation of explanatory laws, the first step in scientific research is the collection and description of facts.
9. It is earth's gravity that ________ people their weight.
10. _______ that new information to anyone else but the sergeant
11. Considered unique and exotic, ________.
12. Perhaps the oldest theories of business cycles are ________ that linked their cause to fluctuations of the harvest.
13. Oscillatona, one of the few plants that can move about, ________ a wavy, gliding motion.
14. The works of Picasso were quite ________ during various periods of his artistic life.
15. The more hemoglobin one has, the more oxygen is carried to ________ cells.
16. ________ can be grown on arid land.
17. ________ air traffic controllers guide planes through conditions of near zero visibility.
18. Culture influences the way ________.
19. Overexposure to the sun causes ________ health problems.
20. The doctor told his receptionist that he would return ________
