Solution Explanation:

A. Over the past 10 years, no pandas have been imported to the United States
--- This supports the conclusion, but a weak support
B. Since there are fewer pandas in the world today than 10 years ago, zookeepers have found it difficult to secure pandas for their zoos, especially since the cost to secure and support the panda is twice that of any other animal.
--- As the cost of securing pandas and supporting them has risen as mentioned in the paragraph, it adds to the already existing premise. Solution
C. The recent drought in China and southeastern Asia has severely decreased the bamboo shoots available for pandas to eat throughout the world.
--- Unrelated
D. A recent study has concluded that the animal people look forward to seeing the most at zoos is the koala bear.
--- Unrelated
E. An increase in the number of zoos throughout the United States has increased the demand for pandas by medium-sized and small zoos.
--- Weak solution, fairly outstretched