The first thing to notice is that the media we're all familiar with--from books to televis

ion--are one-way propositions: they push their content at us. The Web is two-way, push and pull. In finer point, it combines the one-way reach of broadcast with the two-way reciprocity (互惠) of a mid-cast. Indeed, its user can at once be a receiver and sender of broadcast, a confusing property, but mind-stretching!

A second aspect of the Web is that it is the first medium that honors the notion of multiple intelligences. This past century's concept of literacy grew out of our intense belief in text, a focus enhanced by the power of one particular technology--the typewriter. It became a great tool for writers but a terrible one for other creative activities such as sketching, painting, notating music, or even mathematics. The typewriter prized one particular kind of intelligence, but with the Web, we suddenly have a medium that honors multiple forms of intelligence-- abstract, textual, visual, musical, social, and kinesthetic. As educators, we now have a chance to construct a medium that enables all young people to become engaged in their ideal way of learning. The Web affords the match we need between a medium and how a particular person learns.

A third and unusual aspect of the Web is that it leverages (起杠杆作用) the small efforts of the many with the large efforts of the few. For example, researchers in the Maricopa County Community College system in Phoenix have found a way to link a set of senior citizens with pupils in the Longview Elementary School, as helper-mentors (顾问). It's wonderful to see- kids listen to these grandparents better than they do to their own parents, the mentoring really helps their teachers, and the seniors create a sense of meaning for themselves. Thus, the small efforts of the man--the seniors--complement the large efforts of the few--the teachers. The same thing can be found in operation at Hewlett-Packard, where engineers use the Web to help kids with science or math problems. Both of these examples barely scratch the surface as we think about what's possible when we start interlacing resources with needs across a whole region.

What does the word mind-stretching imply？

A．Obtaining one's mental power.

B．Strengthening one's power of thought.

C．Making great demands on one's mental power.

D．Exerting one's mental power as far as possible.