The correct answer is A. granular soil.
Granular soil is the most suitable material for highway embankments because it is strong and stable. It is also relatively easy to work with and can be compacted to a high density. Granular soil is made up of particles of sand, gravel, and crushed stone. These particles are held together by friction and interlocking, which gives granular soil its strength.
Organic soil is not as suitable for highway embankments because it is not as strong or stable as granular soil. Organic soil is made up of plant material, which decomposes over time. This decomposition can cause the soil to become loose and unstable.
Silts and clays are also not as suitable for highway embankments as granular soil. Silts are fine-grained particles that are smaller than sand but larger than clay. Clays are very fine-grained particles that are smaller than silts. Both silts and clays can be difficult to work with and can become unstable when wet.
In conclusion, granular soil is the most suitable material for highway embankments because it is strong, stable, and easy to work with.