Answer:
d. Lobbying offers benefits but must also be carefully monitored.
Step-by-step explanation:
In the first part of the text, Senator Robert Byrd mentions the presence of lobbyists since the creation of Congress and then points out their benefits and significance when he states the following: "We could not adequately consider our work load without them. (...) They all have a service to fulfill." However, Bird also claims that they should be carefully monitored when he highlights "the need for eternal vigilance" of this group.