What is the most important difference between roofs A and B?
a. At headwalls and sidewalls at A, corrosion may spread to metal lathe installed behind stucco, requiring stucco removal for repair, a potentially much more expensive problem than B, in which the roof has no direct interface with the exterior wall-covering materials.
b. Corrosion on A is more widespread and uniform and so is a more serious condition than B.
c. A is intentionally corroded and stable. B is not.
d. A consists of large panels more expensive to replace than the individual shingles covering B.