What ocean layer contains approximately 90% of earth's sea water

 Deep ocean (or below thermocline)

Explanation:

Most of Earth’s seawater (around 90%) is in the deep ocean, located below the thermocline and pycnocline. The deep ocean´s water is colder and denser than other ocean layers.

Because deep waters are not influenced by the wind, they are non-turbulent and homogenous, meaning they have a constant temperature and salinity from place to place.

c. troops marched forward in close formation against newer, more accurate weapons

a and b!

dfroos means which is a and b