Of course developing a system for helping students whose needs are out of the ordinary had been a necessary step in helping those students get into the world of public education.
It is perhaps not an exaggeration to say that we shall soon be trusting our health, wealth and happiness to elements with whose very names the general public are unfamiliar.
2.介词 + which的用法
Children are best served when schools contribute to shaping the solid foundation on which their future will be built.
However, the batteries from which they(electric vehicles) draw energy usually contain harmful chemicals, which become pollutants when the batteries are disposed of.
We are not conscious of the extent to which work provides the psychological satisfaction that can make the difference between a full and an empty life.
Biologists believe that rainforests are the home of perhaps half the world’s biotic species, about five-sixth of which have not yet been described and named.
There are two spare rooms in the building, neither of which has been provided with modern facilities.
(1)as与the same, such, so, as等关联使用。如：
As the forest goes, so goes its animal life.
As is true in all institutions, juries are capable of making mistakes.
As is generally accepted, economic growth is determined by the smooth development of production.
as has been said before, as has been mentioned above, as can be imagined, as is known to all, as has been announced, as can be seen from these figures, as might/could be expected, as is often the case, as has been pointed out,
as often happens, as will be shown等。
(2)先行词是不定代词anything, nothing, little, all, everything时，关系代词用that;
(3)先行词由形容词最高级或序数词修饰或由next，last, only, very修饰时，用that;
There are few teachers but know how to use a computer.
There is no complicated problem but can be solved by a computer.