clear. The Zeiss telescope on the roof is generally open by 7 pm. All observing must be completed by 9：45 pm.

21．What can we learn about Griffith Observatory according to the passage?

　　A．It is open all the year around.

　　B．It is mostly visited at weekends.

　　C．It becomes famous because of Hollywood.

　　D．It is the most attractive place in Los Angeles.

22．Which of the following best describes the Samuel Oschin Planetarium theater?

　　A．Hearing assist devices are provided to seniors.

　　B．The shows there generally last 60 to 90 minutes.

　　C．Visitors are required to be seated before the show starts.

　　D．The tickets for the shows can be bought through the website.

23．To watch the show, a young couple with a 7­year­old son should pay ________.

　　A．$13.00　　　　B．$15.00 C．$17.00 D．$20.00

24．Which of the following is charged?

　　A．Parking. B．Telescopes. C．Hearing assist devices. D．Watching presentations.

　　Shopping centers, stadiums and universities may soon have a new tool to help fight crime.

　　A California company called Knightscope says its robots can predict and prevent crime. Knightscope says the goal is to reduce crime by half in areas the robots guard.

　　William Santana Li is the chief executive officer of Knightscope. He says, "These robot security guards will change the world. Our planet has seven billion people on it. It's going to quickly get to nine billion people. The security equipment that we have globally is just not going to develop that fast. The company's Autonomous Data Machines can become the eyes and ears of law enforcement (执行)．"

　　"You want it to be machines plus humans. Let the machines do the heavy and sometimes dangerous work and let the humans do the strategic decision­making work, so it's always working all together."

The machines are one and a half meters tall and weigh 136 kilograms. They do not carry weapons but they have day and night time video cameras which are able to turn 360 degrees