Ineed :
(1) a social dilemma is a situation in which the most rewarding short-term choice for an individual will ultimately lead to negative outcomes for all concerned. (2) for example, as you hike along a beautiful mountain trail, you stop for a snack. (3) you are tempted to throw away your empty water containers and granola bar wrappers, knowing that your backpack will be lighter if you don’t have to carry your trash to the top of the mountain and back. (4) but you hesitate, knowing that if all hikers litter the trail, it will soon be unpleasant for all who use it. (5) or consider the situation of many communities in the southwest that have suffered severe drought for years, so that water conservation is essential. (6) individuals living in such drought-stricken areas face personal decisions. (7) for instance, should i forgo the pleasure of a long shower today so that there will be more water for all in the future?

1. the main idea is expressed in sentence

a. 1.

b. 2.

c. 4.

d. 7.