Why Are "Old Fashioned" Filibusters Rare Occurrences in Today's Senate

Why are "old fashioned" filibusters rare occurrences in today's Senate?

A) Few senators are willing to endure the physical challenges of mounting a traditional filibuster.
B) Leaders tend to seek unanimous consent to freeze a filibustered bill and move on with other business.
C) Most senators will seek alternate methods of stopping a bill before resorting to a filibuster.
D) Party leaders strongly discourage filibusters.
E) Senators usually do not feel strongly enough about a bill to filibuster.