The Files of X-Ray Structures Available in the Protein Data

The files of x-ray structures available in the Protein Data Bank, PDB, list a B factor, known as a temperature factor. This factor describes ___________________.
I. how large a biomolecule is
II. how strong the interactions between the chains are
III. how much flexibility various loops have in the structure
IV. how much thermal motion there was in the crystal in various regions
V. linearity of the molecule

A) I and II
B) II and III
C) III and IV
D) I and V
E) II and V