Let me jump in here and pick up where hero left off (nice job hero!):
First let's address answer choice E. This is an assumption question, so the answer needs to be something that if you take it away, the conclusion is not merely weakened, but becomes very unlikely. Let's see what happens when answer choice E is negated. "Energy-efficient technologies based on new scientific principles will be introduced in the next 50 to 100 years." The portion in bold makes this answer choice not as good of an option. You see, answer choices that are too specific are not good for assumption questions. What if energy efficient technologies are created based on existing scientific principles, like wind power and good insulation? Another problem is that it is not necessary that new technologies be introduced at all if existing technologies can spread and help to reduce consumption.
Now let's look at answer choice A. A says"Technology used to make buildings energy efficient will not become prohibitively
expensive over the next century." If this answer choice is taken away - negated - then we see that technology (current or future it does not matter which) used to make buildings energy efficient will become prohibitively expensive...Prohibitively expensive means so expensive that people cannot afford to use it. This will truly damage the conclusion that efficiency will save $200 billion dollars per year in the future.
Are there still questions?
