已知a、b、c是直线，β是平面，给出下列命题：
①若a⊥b，b⊥c，则a∥c；
②若a∥b，b⊥c，则a⊥c；
③若a∥β，b⊂β，则a∥b；
④若a与b异面，且a∥β，则b与β相交；
⑤若a与b异面，则至多有一条直线与a，b都垂直．其中真命题的个数是（ ）
A．1
B．2
C．3
D．4
①不正确，a与c可能相交或异面；②正确，由等角定理判断；
③不正确，a与b无公共点，它们平行或异面；
④不正确，只要有一条直线l和a、b垂直，则与l平行的直线都满足．
故选A．．
| 完型填空。 | |||
| Mr. Glen is a millionaire. Five years ago, after returning from abroad to his motherland, he 1 up his small company. Speaking of success, Glen often tells us a story about his 2 expensive "school" fees. He always owes his success to it. At that time, Glen, who already got a Ph. Degree, decided to return to the homeland, starting a company. Before 3 , he bought a Rolex watch with the 4 made through years of work after school and the scholarships. At the airport he had to accept the routine customs check. The watch on his wrist was also demanded to be 5 down for inspection. Glen knew that carrying the 6 goods out had to pay the tax. And he worried about paying 7 for his watch. So when he was checked, he told a lie that his watch was a worthless 8 . When he was 9 of his "smarts", immediately, 10 the presence of Glen, the officers hit the watch, which 11 nearly ￥100,000, into pieces at hearing Glen's words. Glen was amazed. 12 he understood why, he was taken to the office to be 13 strictly. For many times of entryexit 14 he knew that only those people in the "blacklist" would "enjoy" this special treatment. The officers looked out every thing carefully in the box, and warned him 15 time of entry and exit he must accept the check and if 16 reusing and carrying fake and shoddy (劣质的) goods, he would be charged according to law! Suddenly, his face turned red, and he had nothing in mind after 17 the plane for long. After returning to the homeland, he often told the story to his family, and his employees, too. He said that this made a deep 18 on him, because an additional high "school" fee that he had ever paid made him realize the value of 19 , which he would 20 as the secret of his success forever. | |||
| ( )1. A. set ( )2. A. good ( )3. A. staying ( )4. A. books ( )5. A. put ( )6. A. ordinary ( )7. A. one ( )8. A. present ( )9. A. afraid ( )10. A. in ( )11. A. paid ( )12. A. Before ( )13. A. appreciated ( )14. A. conditions ( )15. A. no matter what ( )16. A. came out ( )17. A. landing ( )18. A. expression ( )19. A. honesty ( )20. A. remember | B. came B. bad B. leaving B. things B. looked B. common B. it B. trade B. proud B. on B. spent B. After B. beaten B. experiences B. no matter how B. found out B. flying B. idea B. lies B. learn | C. went C. extra C. living C. saving C. taken C. specific C. them C. toy C. well C. before C. took C. If C. spoken C. experiments C. no matter when C. sent out C. catching C. thought C. goods C. revise | D. called D. few D. coming D. pounds D. lied D. many D. these D. fake D. hard D. after D. cost D. Though D. examined D. chances D. no matter why D. set out D. boarding D. impression D. things D. read |