Here it says, identify all hydrophobic amino acids. Now remember, when they say hydrophobic, they're really just saying, which one represents non-polar amino acids? Remember, our memory tool here will be GAV, TRIP, FOUL, LIMPING. So here, if we take a look at these images, A would be a hydrophobic amino acid, because it represents the P within our memory tool. This is proline. Remember, it can be identified by its R group, which is this cyclic portion that actually encompasses the amino group.
Then what else do we have? We don't recall seeing one which is CH₂OH, so that's out. We don't recall seeing one with just one ring with an NH group in it, so that's also out. Now this last one here, its R group is a hydrocarbon, so for sure it's non-polar because hydrocarbons are non-polar. This one here will represent isoleucine. So, isoleucine. So out of the options here, it's both A and D. Both of them have non-polar R groups, and therefore, represent hydrophobic amino acids. So those would be our final answers.