Originally posted by wormer
Monomeric single pass transmembrane protiens span with a membrane with a single alpha helix that has characteristic chemical properties in the region of the bilayer. Which of the following a.a. Sequences are most suited for such a transmembrane segment?
The problem with this is that it requires one to actually know how the amino acid sequences are meant to go. After looking at Wikipedia I found a paper  which mentions that hydrophobic radicals tend to be clustered in the n, n+3, n-3, n+4, and n-4 positions in its abstract. Given that the offsets your question gives has these offsets I'd guess choose hydrophobic ones. The Wikipedia page  conveniently has a table with a hydrophobic scale. The amino acids at positon 3, 6, 9, 12, 15, and 18 have index L = 3.8, F = 2.8, M = 1.9, V = 4.2, T = -0.7, L = 3.8. The ones at position 4, 8, 12, 16 have indices I = 4.5, V = 4.2, V = 4.2, and I = 3.8. If I'm right in thinking that these numbers should all be as large as possible then the correct answer is A. If they should be as negative as possible then the correct answer is C. This is a complete guess based on what it said in the article  and Wikipedia and I can easily have latched onto the wrong thing, but I think it is A, the first row.