Answer :
A "Shared environment influence", they aren't currently in a shared environment. B,fraternal would be like brotherly influence, which is clearly wrong if we're focusing on their time apart. D, what would the teachers have to do with their genetic influence? they aren't related to the identical twins (not that we know of). so that leaves C: this would be the most likely considering their environment (their surroundings?) are different {nonshared environmental influence}. im not certain though.