Why Do Lobbying Firms Often Hire Former Members of Congress

Why do lobbying firms often hire former members of Congress?

A) Powerful party leaders pressure lobbying firms to do so.
B) Former members of Congress will work more cheaply because of their
Government pension.
C) Doing so makes it less likely that the group will be audited or investigated by federal agencies like the Internal Revenue Service.
D) Former members of Congress can provide the group with important information, such as what kinds of policies individual legislators will support.
E) Former members of Congress are typically wealthy and willing to contribute large sums of money to the lobbying firm when hired.