问题 选择题

某人在广场上练习驾驶汽车,两次拐弯后,行驶方向与原来相同,这两次拐弯的角度可能是(        )

A.第一次左拐30°,第二次右拐30°

B.第一次右拐50°,第二次左拐130°

C.第一次右拐50°,第二次右拐130°

D.第一次向左拐50°,第二次向左拐120°

答案

答案:A

题目分析:两次拐弯后,行驶方向与原来相同,说明两次拐弯后的方向是平行的.对题中的四个选项提供的条件,运用平行线的判定进行判断,能判定两直线平行者即为正确答案.

如图所示(实线为行驶路线):

A符合“同位角相等,两直线平行”的判定,其余均不符合平行线的判定.

故选A.

点评:平行线的判定和性质是初中数学的重点,贯穿于整个初中数学的学习,是中考常见题,一般难度不大,需熟练掌握.

多项选择题
单项选择题

The dot-com collapse may have been a disaster for Wall Street, but here in Silicon Valley, it was a blessing. It was the welcome end to an abnormal condition that very nearly destroyed the area in an overabundance of success. You see, the secret to the Valley’s astounding multiple-decade boom is failure. Failure is what fuels and renews this place. Failure is the foundation for innovation.
The valley’s business ecology depends on failure the same way the tree-covered hills around us depend on fire--it wipes out the old growth and creates space for new life. The valley has always been in danger of drowning in the unwelcome waste products of success--too many people, too expensive houses, too much traffic, too little office space and too much money chasing too few startups. Failure is the safety valve, the destructive renewing force that frees up people, ideas and capital and recombines them, creating new revolutions.
Consider how the Internet revolution came to be. After half a decade of start-up struggles, for example, hundreds of millions of Hollywood dollars were going up in smoke. It all seemed like a terrible waste, but no one noticed that the collapse left one very important byproduct, a community of laid-off C++ programmers who were now expert in multimedia design, and out on the street looking for the next big thing.
These media geeks were the pioneer of the dot-com revolution. They were the Web’s business pioneers, applying their newfound media sensibilities to create one little company after another. Most of these start-ups failed, but even in failure they advanced the new medium of cyberspace. A few geeks, like Silicon Graphics founder Jim Clark, succeeded and utterly changed our lives. In 1994 Clark was unemployed after leaving the company be founded, doggedly trying to develop a new interactive-TV concept. He approached Marc Andreessen, the co-developer of Mosaic, the first widely used Internet browser, in hope of persuading Andreessen to help him de-sign his new system. Instead, Andreessen opened Clark’s eyes to the Web’s potential. Clark promptly tossed his TV plans in the trash, and the two co-founded Netscape, the cornerstone of the consumer-Web revolution.
Like the interactive-TV refugees and generations of innovators before them, the dot comers are already hatching new companies. Many are revisiting good ideas executed badly in the’ 90s, while others are striking out into entirely new spaces. This happy chaos is certain to mature into a new order likely to upset an establishment, as it delivers life-changing wonders to the rest of us. But this is just the start, for revolutions give birth to revolutions. So let’s hope for more of Silicon Valley’s successful failures.

The author writes of the experiences of Jim Clark to demonstrate

A.the hardships a web pioneer must go through.

B.the trouble in which Clark was caught.

C.the role failures positively play in revolutions.

D.the cooperation among dot-comers.