Why Are Compromises Difficult to Come by Between Congress and the President

Why are compromises difficult to come by between Congress and the president?

A) The president's agenda is often unrealistic, and Congress refuses to implement any policies from it.
B) Congress is not beholden to the president's policy agenda and often has its own agenda to implement.
C) Presidents have been difficult to work with an unbending when presented with compromises.
D) Credit for enacting a successful program is rarely shared equally, which creates tension.