31. What is the current expert consensus concerning the role of acid rain on the health of forests?
A. Acid rain is indisputably responsible for the declining health of many forests.
B. Acid rain is not responsible for any of the decline observed in many forests.
C. Acid rain is believed to weaken trees, leaving them susceptible to disease, insects, etc.
D. There is not sufficient evidence that there has been an appreciable decline in the health of any forests.