Why Do Members of Congress and Their Staffers Sometimes Rely

Why do members of Congress and their staffers sometimes rely on interest groups to act as proxy staffers?

A) Congressmen and Congresswomen tend to share goals with the interest groups they work with, and interest groups can provide expertise useful in the legislative drafting process.
B) Congressional offices are often understaffed and know that experts from interest groups cannot afford to offer biased information to legislators.
C) Congressional offices are more likely to grant access to groups with clear ideologies than constituent groups.
D) When Congressmen and Congresswomen are subjected to "cross pressure" from interest groups and constituents, they tend to side with interest groups.
E) When Congressmen and Congresswomen are subjected to "cross pressure" from interest groups and constituents, they tend to side with their constituents' public opinion.