The greatest threat to our planet is that is the belief that someone else will save it
essay in 1000 words

The planet earth where we are living in the present century is facing alot of problems and they are becoming so serious that it will be difficult for the habitual of the earth to survive
The main reason is the global warming  that is 
submerging many low-lying islands in the ocean.
pollution is so  high that there are rare place to breathe a clean air
the life on earth is dwindling forests are continuously decreasing and amount of oxygen also decreasing
After listening to these problems there must be some remedy for them
we dont have to rely on others for  solution
we have to work by own ,have to feel our responsibilities to save our planet
every one of us should avoid polluting it and have to grow as many plants as we can and have to recycle the waste because every drops contribute to make a river

Ithink the answer is b. shakeri hope im not wrong : )