Which source would be most helpful in researching this question?

" Does social networking provide the same benefits for seniors as off-line communities?"

A. A documentary titled Grandma's on Facebook: Keeping Elderly Americans Connected
B. A website with instructions and advice about various social media platforms
C. A magazine article titled "Aging and the Effects of Sedentary Behaviors"
D. A diary written by a very popular and active senior citizen during the Great Depression