Which of the Following Represents a Common Bias Found in the Research

Which of the following represents a common bias found in the research regarding social networks and older adults?

A) The research has focused mostly on women.
B) The research has focused mostly on men.
C) The research has focused more on the quality and quantity of social networks than on the health benefits.
D) The research tends to focus more on the frequency of contact than the quality of the relationships.