在此句中,the +单数可数名词,表示类别,不是the+adj.
the+单数可数名词,表示的含义是一类,但是形式是单数,所以其谓语动词依然是用is。
后面的the student也是类别。
The teacher is responsible for the student's success......
=Teachers are responsible for students' success......
注意:可数名词的复数也可以表示类别。
因此第二句中的They=Teachers
They are only there ...
=Teachers are only there ...
the teacher是特指