Indoor pollution experts conducted an analysis of the paint used in many office buildings which revealed that the paint contains traces of lead. The lead seems to rise to the surface of the paint and escape into the building's air supply. Tests show that because of the chemical drying process, the lead is not discernible on the surface until the paint has been on the walls for at least six months. To meet safety standards, owners should repaint walls at least every six months, or cover the walls with a different material.

Which of the following, if true, would most weaken the conclusion above?

A) The indoor pollution experts had no clear understanding of why it took six months for the lead to become discernible on the paint's surface.
B) The indoor pollution experts neglected to examine the paint for traces of other toxic substances such as cadmium and mercury.
C) The amount of lead found on the surface of the paint after six months remained constant for the next two years.
D) The indoor pollution experts found that even in those offices painted with a different brand of paint, traces of lead were still found in the air workers breathed.
E) The indoor pollution experts' research shows that the amounts of lead that come into contact with the air people breathe, even in the office buildings that used the greatest amount of paint, are too low to affect workers.

E is the answer. here is the approach.

conclusion : office buildings need to have walls repainted every six months or covered with different materials to meet the safety standard

premise : lead is not discernible on the surface until six months later.

assumption : after six months, the lead that is discernible on the surface will negatively impact on the safety of people breathing the air in the building

negative rephrasing - negate the conclusion and have this 'office building managers might not need to have the walls repainted or covered with different materials because...'

review the answers:
a. doesn't follow the negative rephrasing
b. doesn't follow the negative rephrasing
c. irrelevant
d. support the conclusion
e. CORRECT - support the negative rephrasing