Answer: C. about 3%
Explanation:
In 2006 , Number of dogs in U.S. dogs = 72 million
In 2010, Number of dogs in U.S. dogs = 70 million
The percent decrease in the number of dogs in U.S. Homes from 2006 to 2010 =

So, the percent decrease in the number of dogs in U.S. Homes from 2006 to 2010 was about 3%.
Hence, the correct option is C. about 3%