Critical Reasoning (CR) | Re: Many office buildings designed to prevent outside air from entering

air in other office buildings does not have elevated levels of these substances, eventhough those buildings are the same age as the "sick" buildings and have similar designs and ventilationsystems .

They have similar ventilation systems, which points to both of them having windows that can be opened. Since both have windows that can be opened, we still need a reason to explain why some buildings have more toxic air.
So E although extremely tempting, does not help explain the difference.

(A) on the other hands does explain why some buildings have toxic air, as they use certain substances that produce toxic flames.

Hope thishelps!