In Many Middle Eastern Countries,showing Someone the Bottom of Your

In many Middle Eastern countries,showing someone the bottom of your foot or shoe is considered very rude,so American military personnel stationed in the Middle East are instructed to keep their feet inside helicopters when flying low.Why is this instruction needed?

A) The meaning of gestures is not universal.
B) Soldiers are generally rude and need specific instructions to keep them from offending civilians.
C) Americans speak a different language than Middle Easterners.
D) The sanctions used to achieve social control are very different in America and the Middle East.