Choose the correct answer from the list below. Not all of the answers will be used.
-The first step in protein purification from a homogenate is usually ____________.

A)HPLC
B)specific activity
C)MALDI-TOF mass spectrum
D)gradient centrifugation
E)proteome
F)SDS
G)two-dimensional electrophoresis
H)Svedberg
I)immunoglobulin
J)differential centrifugation
K)overlap peptides
L)affinity chromatography