Why Might Integral Membrane Proteins Be Difficult to Study Based

Why might integral membrane proteins be difficult to study based upon what you know of their amino acid composition?

A) They are difficult to isolate in soluble form due to their hydrophobic transmembrane domains.
B) They are difficult to isolate in soluble form due to their hydrophilic transmembrane domains.
C) They are too small.
D) They are too large.
E) None of these are correct.