新东方新托福听力特训Windows

Windows usually look like they’re all made of glass and wood. However, there is more to windows
than meets the eye. Things that look like “wood” could be aluminum, vinyl or some other
composite material. As people prefer things that are “low-maintenance”, there has been an
explosion in materials that look like wood being used for frames; they don’t need sanding and
painting and still look like high quality wood. Sometimes a layer of aluminum is used to coat the
exterior surfaces of a window to provide a long-lasting., low-maintenance surface. It is called
“cladding”. I think I should write down the word on the board. It refers to the application of one
material over another to provide a weather-proof layer. For aluminum there are fewer color
options than with wood finishes and usually the thicker the aluminum is the more durable it is.
However, it doesn’t have the insulating qualities of windows made of other materials so they’re not
widely used. Vinyl is another popular low-maintenance option. It can also be applied over other
materials, like wood or wood products. Like aluminum, the thicker the vinyl the more durable it
will be. Composite windows and vinyl windows are gaining popularity nowadays as non-wood,
energy efficient and low-maintenance alternatives which don’t warp or rot like wood windows can
in extreme conditions.

Why does the professor say this?

A The professor thinks that it is necessary to remind students of its spelling.
B The professor thinks that it is the most important term in the lecture.
C The professor thinks that students do not know the term.
D The professor fells that it is necessary to use the board more often.
(C)