About percent of u.s. 18- to 29-year-olds use social networking sites to keep in contact

Base on the research studies that has been made in regards with social networking sites, it has been found out that eighty six percent in the United States who are in the age of eighteen to twenty nine year olds uses the social networking site while the remaining thirty four percent are in the age of sixty five years old and above.

The answer to the first one is actually D: The development of more efficient modes of transportation. The second one is C.