On Average, How Many Amino Acids, Forming a Hydrophobic $\alpha$ -Helix, Does It Take to Cross the Hydrophobic Part of -Helix

Multiple Choice

On average, how many amino acids, forming a hydrophobic $\alpha$ -helix, does it take to cross the hydrophobic part of the membrane?

A) about 10 amino acids
B) about 20 amino acids
C) at least 40 amino acids
D) about 2-3 amino acids
E) None of these are correct.