Read the following SAT test question and then click on a button to select your answer.

If the function f is defined by f(x)=(x-a)(x-b)/(x-c), where 0<a<b<c, for which of the following values of x is f undefined?

I.a
II.b
III.c

(A) None
(B) I only
(C) III only
(D) I and II only
(E) I,II and III

来源:可可英语 http://www.kekenet.com/sat/201404/292961.shtml