The correct answer is D.
Group index (GI) is a measure of the soil’s ability to support a pavement. It is determined by a laboratory test that measures the soil’s strength and drainage characteristics. The higher the GI, the better the soil’s ability to support a pavement.
CBR, or California Bearing Ratio, is a measure of the soil’s ability to support a load. It is determined by a field test that measures the soil’s resistance to penetration. The higher the CBR, the better the soil’s ability to support a load.
The thickness of a pavement is determined by the soil’s GI and CBR. The higher the GI and CBR, the less thickness of pavement will be required.
Therefore, all of the statements are correct.