完形填空。 It seems like everywhere a person goes there is at least one person with a cell phone to his ear. Even in places 1 cell phone usage is banned such as concert halls or movie theatres there is the 2 offender, or at least a few people using the text messaging feature 3 their phones. Cell phone usage has 4 over the past decade and continues to rise. Nearly 200 5 people in the United States have cell phones and there are 6 over one billion users worldwide. That means there are a lot of phones 7 their frequencies over the airwaves at any given time. Concern has arisen over whether or not cell phone usage 8 harm a person's health. Brain cancer rates in the United States have risen since call phones were 9 , leading some people to wonder if cell phone usage is the reason for the 10 . Some people say the biggest danger 11 cell phones isn't from the either real or perceived potential to develop cancer, but from 12 while using the cell phone. How many of us have seen vehicles driving 13 erratically (不稳定地) down the road. And we often see when we get near the vehicle the driver on a cell phone is 14 on a cell phone. It is a proven fact that a driver on a cell phone is 15 attentive and more likely to get in an accident. And, hands-free sets aren't the 16 that some people may believe. Yes, they 17 both hands for driving and prevent a person from getting a sore (酸疼的) arm, 18 the driver's mind is still 19 the conversation and therefore less attentive to what is 20 around him or her on the road. (     )1. A. which (     )2. A. busy (     )3. A. under (     )4. A. been exploded (     )5. A. millions (     )6. A. well (     )7. A. delivering (     )8. A. may (     )9. A. allowed (     )10. A. increase (     )11. A. with (     )12. A. attention (     )13. A. quite (     )14. A. using (     )15. A. more (     )16. A. problem (     )17. A. hold up (     )18. A. therefore (     )19. A. taken up (     )20. A. happening to B. where B. always B. on B. exploded B. millions of B. good B. carrying B. must B. invented B. decline B. before B. attractive B. almost B. talking B. less B. question B. pick up B. as B. filled by B. going on C. there C. occasional C. from C. been exploding C. million C. better C. taking C. can C. introduced C. improvement C. in C. careless C. hardly C. moving C. least C. mean C. put up C. but C. occupied with C. talking about D. here D. occasionally D. to D. exploding D. million of D. best D. sending D. should D. bought D. rose D. on D. inattentiveness D. nearly D. handing D. fewer D. answer D. free up D. though D. picked up D. moving about