[填空题]Scientists believed that Mayan city ______ because many buildings were left unfinished.

[填空题]Scientists believed that Mayan city ______ because many buildings were left unfinished.

[简答题]Observational Learning
Some scientists believed that direct reinforcement could not account for all types of learning. Bandura’s learning theory added a social element, arguing that people can learn new information and behaviors by watching other people. Known as observational learning (or modeling), this type of learning can be used to explain a wide variety of behaviors. Observational learning takes place when an individual acquires a habit or skill through witnessing the performance of another person. Such learning often, but not always, involves imitation of the observed activities.
Question: The professor uses an experiment to illustrate the definition of "observational learning". Explain how this example is related to the reading passage.

[填空题]Many scientists believed that they could produce an anti-AIDS vaccine that could be given to people to ______the disease.

[单项选择]Scientists have long believed that constructing memories is like playing with neurological toys. Exposed to a barrage of sensations from the outside world, we connect together brain cells to form new patterns of electrical connections that stand for images, smells, touches and sounds.
The most unshakable part of this belief is that the neurons used to build these memory circuits are depletable resource, like petroleum or gold. We are each given a finite number of cells, and the supply gets smaller each year. That is certainly how it feels as memories blur with middle age and it gets harder and harder to learn new things. Maybe it’s time for this notion to be forgotten-or at least radically revised.
In the past two years, a series of confusing experiments has forced scientific researchers to rethink this and other assumptions about how memory works. The perplexing results of these experiments remind scientists how much they have to learn about one of the last great mysteries-h
A. The neurons used to build the memory are a depletable resource.
B. The reason of memory loss as one grows older is that the neurons are worn out with the increase of age.
C. New memories do not need the supply of new neurons in the brain.
D. All of above.

[单项选择]Mars fascinates scientists because of its similarity to Earth, and it fascinates the public because our myth of "Martians" is a vision of life beyond Earth. The Mars 62 continues with the launch of a robot vehicle by UK scientists. It’s part of a project to build an "autonomous robotic scientist" to 63 the Martian surface and is key to the European Space Agency’s 2011 ExoMars 64 .
The six-wheeled vehicle housing a myriad of scientific 65 and detectors is the Mars rover, nicknamed "Bridget". Astrium, an EADS company, are 66 the ExoMars rover prototype and coordinating its 67 with other UK-based institutions.
Searching for a 68 similar to that found on Mars, the team took the rover to El Teide National Park in Tenerife. Lester Waugh, leading the EADS Astrium team, explains, "The rover’s not waterproof so the conditions need to be dry as any moisture affects the way the sand 69 unde
A. aviation
B. pilot
C. guidance
D. navigation