He was so convinced that people were driven by ______ motives that he could not believe that anyone could be unselfish.

A．selfless

B．personal

C．ulterior

D．remarkably

Watch a baby between six and nine months old, and you will observe the basic concepts of geometry being learned. Once the baby has mastered the idea that space is three-dimensional, it reaches out and begins grasping various kinds of objects. It is then, from perhaps nine to fifteen months, that the concepts of sets and numbers are formed. So far, so good. But now an ominous development takes place. The nerve fibers in the brain insulate themselves in such a way that the baby begins to hear sounds very precisely. Soon it picks up language, and it is then brought into direct communication with adults. From this point on, it is usually downhill all the way for mathematics, because the child now becomes exposed to all the nonsense words and beliefs of the community into which it has been so unfortunate as to have been born. Nature, having done very well by the child to this point, having permitted it the luxury of thinking for itself for eighteen months, now abandons it to the arbitrary conventions and beliefs of society. But at least the child knows something of geometry and numbers, and it will always retain some memory of the early halcyon days, no matter what vicissitudes it may suffer later on. The main reservoir of mathematical talent in any society is thus possessed by children who are about two years old, children who have just learned to speak fluently.

What does the passage mainly discuss？

A．How basic concepts of physics are learned.

B．Math-learning strategies for babies.

C．How basic concepts of physics are learned.

D．Math-learning strategies for babies.

Which of the following pairs of terms does the author regard as most nearly synonymous？

A．Solar and extraterrestrial.

B．Photovoltaic devices and solar cells.

C．Crystalline silicon and amorphous materials.

D．Amorphous materials and higher efficiencies.

The author mentions which of the following as advantages of amorphous materials for solar ceils over silicon crystals？

A．The relative thinness of amorphous materials.

B．The cost of amorphous materials.

C．The size of solar cells which can be made of amorphous materials.

D．All of the above.

The tone of the passage can best be described as ______.

A．analytical and optimistic

B．biased and unprofessional

C．critical and discouraged

D．tentative and inconclusive

By dint of much practice, he became ______ and was able to sign his name with either hand.

A．practical

B．tricky

C．ambiguous

D．ambidextrous