Which factor can exacerbate stress corrosion cracking?

The correct choice is the presence of moisture and tensile stress because these two elements are fundamental contributors to the phenomenon of stress corrosion cracking. Stress corrosion cracking occurs when a susceptible material, often in a tensile stressed state, is exposed to a corrosive environment, typically involving moisture. The simultaneous presence of these factors accelerates the cracking process, as moisture can facilitate the electrochemical reactions that contribute to corrosion while tensile stress promotes crack propagation.

Low environmental temperature typically reduces the rate of chemical reactions, which can, in fact, limit corrosion processes; thus, it would not exacerbate cracking. High humidity with low stress levels does not create the conditions necessary for stress corrosion cracking since lower stress levels would not intensify the failure. Excessive material thickness can also serve as a barrier to crack propagation, slowing down the overall process, and therefore would not necessarily lead to exacerbation of stress corrosion cracking as it relates more to the thickness being a factor that affects the whole mechanical stability rather than the specific interaction of stress and corrosion.