根据下面资料，回答题
With the world´ s population estimated to grow from six to nine billion by 2050, researchers,businesses and governments are already dealing with the impact, this increase will have on every-thing from food and water to infrastructure (基础设施) and jobs. Underling all this（46）will be the demand for energy, which is expected to double over the next 40 years.
Finding the resources to meet this demand in a（ 47）, sustainable way is the cornerstone(基石) of our nation´ s energy security, and will be one of the major.（48）of the 21 st centu-ry. Alternative forms of energy-bio-fuels, wind and solar, to name a few--are（49）being funded and developed, and will play a growing（50）in the world´ s energy supply. But ex-perts say that even when（51）, alternative energy sources will likely meet only about 30% of the world´ s energy needs by 2049.
For example, even with（ 52）investments, such as the $ 93 million for wind energy de-velopment（53）in the American Recovery and Reinvestment Act, important alternative ener-gy sources such as wind and bio fuels（54）only about 1% of the market today.
Energy and sustainability experts say the answer to our future energy needs will likely come from a lot of（ 55）--both traditional and alternative.
A．stable
B．solutions
C．significant
D．role
E．progress
F．marvelous
G．included
H．growth
I．exactly
J．consist
K．comprise
L．competitions
M．combined
N．challenges
O．Certainly
第（46）题选