Which one of the following assumptions must be made in order for the author ... ...

Which one of the following assumptions must be made in order for the author to be correct in drawing the conclusion stated in the passage?
(A) Thirty percent of the residential carbon monoxide gauges have been installed within the last fifteen years.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Exercise (Inductive Reasoning)