Secondary school students achieve broad mastery of the curriculum if they are taught with methods appropriate to their learning styles and they devote significant effort to their studies. Thus, if such broad mastery is not achieved by the students in a particular secondary school, those students are not being taught with methods appropriate to their learning styles.
There are
two events, taught with methods appropriate to their learning styles and devote significant effort to studies
Conclusion: if such broad mastery is not achieved by the students in a particular secondary school, those students are not being taught with methods appropriate to their learning styles
It is subtle to capture, by one event, it is decided "broad mastery is not achieved". This is important to observe, events are correlated, not independent.
The conclusion can be properly drawn if which one of the following is
assumed?
(A) As long as secondary school students are taught with methods appropriate to their learning styles, they will devote significant effort to their studies. -> So, the second event is correlated. It makes sense. Let's keep it.
(B) Even if secondary school students are taught with methods appropriate to their learning styles, they will not achieve broad mastery of the curriculum if they do not devote significant effort to their studies. -> It makes both event independent, but conclusion hints of correlated events. Incorrect.
(C) Secondary school students do not achieve broad mastery of the cuniculum if they are not taught with methods appropriate to their learning styles. -> There is no assumption here. Incorrect.
(D) Teaching secondary school students with methods appropriate to their learning styles does not always result in broad mastery of the curriculum by those students. -> Irrelevant.
(E) Secondary school students who devote significant effort to their studies do not always achieve broad mastery of the curriculum.-> Irrelevant.
So, I think A.