The filibuster a. was rarely used throughout most of American history but has become a frequently used tactic in the U. S. Senate during the last 20 years. b. has never been a frequently used tactic in the U. S. Senate. c. has always been a frequently used tactic in the U. S. Senate. d. was a frequently used tactic in the U. S. Senate throughout most of American history but has almost never been used during the last 20 years. 1 points Save Answer