4) What made the war difficult for the US army and troops fighting in the war? a. The jungle conditions b. Ambushes and traps c. All of the above d. None of the above

Not sure which war you’re asking about. If Vietnam, then c is your answer.

Ifound the exercise on the internet. attached is the list mentioned above.in order for a compound to be considered optically active it can't have any axis or plan of symmetry. the molecule  shouldn't also  be superimposable on its mirror image.with such considerations, the compounds that are optically active are: -third compound on the first image is optically active; -second and third compound from the second image are optically actives.