Which of the following is a true statement?
A. Sister chromatids are held together by condensins.
B. Ligation and hydrogenation are the most common ways cells regulate the activity of a protein.
C. The first readily visible sign that a cell is about to enter the S phase is ubiquitylation of chromosomes.
D. In a typical somatic cell, interphase is the longest phase of the cell cycle.
E. The cell-cycle control system depends on cyclically activated carrier GTP molecules.