Critical Reasoning

In Western economies, more energy is used to operate
buildings than to operate transportation. Much of the
decline in energy consumption since the oil crisis of
1973 is due to more efficient use of energy in homes
and offices. New building technologies, which make
lighting, heating, and ventilation systems more
efficient, have cut billions of dollars from energy
bills in the West. Since energy savings from these
efficiencies save several billion dollars per year
today, we can conclude that 50 to 100 years from
now they will save more than $200 billion per year
(calculated in current dollars).
On which one of the following assumptions does the
argument rely?
(A) Technology used to make buildings energy
efficient will not become prohibitively
expensive over the next century.
(B) Another oil crisis will occur in the next 50 to
100 years.
(C) Buildings will gradually become a less
important consumer of energy than
transportation.
(D) Energy bills in the West will be $200 billion
lower in the next 50 to 100 years.
(E) Energy-efficient technologies based on new
scientific principles will be introduced in the
next 50 to 100 years.