The SCF ubiquitin ligase can recognize and mark various target proteins at different stages of the cell cycle. In this complex, …

A) different F-box subunits recognize different target proteins.
B) the F-box subunit and the E2 ubiquitin-conjugating enzyme are at the opposite ends of the C-shaped molecule.
C) a scaffold protein arranges the other subunits such that the two ends of the complex are separated by a gap.
D) the use of interchangeable parts such as the F-box subunits makes economical use of the genetic information and allows for rapid evolution of new functions.
E) All of the above.