How did farmers primarily protect themselves from invaders during the Han dynasty?

They built brick homes to keep safe from nomads.
They paid taxes in crops in exchange for protection.
They grew silkworms and traded them for weapons.
They lived in small villages to avoid attracting enemies.

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.