13. Houses built during the last ten years have been
found to contain indoor air pollution at levels that
are, on average, much higher than the levels found
in older houses. The reason air-pollution levels are
higher in the newer houses is that many such houses
are built near the sites of old waste dumps or where
automobile emissions are heavy.
Which of the following, if true, calls into question
the explanation above?
(A) Many new houses are built with air-filtration
systems that remove from the house pollu-
tants that are generated indoors.
(B) The easing of standards for smokestack emis-
sions has led to an increase in air-pollution
levels in homes.
(C) New houses built in secluded rural areas are
relatively free of air pollutants.
(D) Warm-weather conditions tend to slow down
the movement of air, thus keeping pollution
trapped near its source.
(E) Pressboard, an inexpensive new plywood substi-
tute now often used in the construction of
houses, emits the pollutant formaldehyde into