The correct answer is option 'D', sensitivity.

Explanation:
Shear strength is the ability of a soil to resist shear stress. It is an important factor in geotechnical engineering as it determines the stability and behavior of soil under different loading conditions. The shear strength of soil can vary depending on its state and condition.

Undisturbed soil refers to soil that has not been altered or disturbed from its natural state. Remoulded soil, on the other hand, refers to soil that has been disturbed and altered through various processes such as excavation, compaction, or mixing.

The ratio of the shear strength of undisturbed soil to that of remoulded soil is known as the sensitivity of the soil. Sensitivity is a measure of how much the shear strength of soil changes when it is remoulded or disturbed. It is an important parameter to consider in geotechnical engineering as it affects the stability and behavior of soil.

Higher sensitivity indicates a greater difference in shear strength between undisturbed and remoulded soil. This means that the shear strength of the soil is more sensitive to disturbance or alteration. Lower sensitivity indicates a smaller difference in shear strength between undisturbed and remoulded soil.

Sensitivity is often used to assess the potential for soil instability or failure. Soils with high sensitivity are more prone to shear failure and are considered less stable. On the other hand, soils with low sensitivity are more stable and less likely to experience shear failure.

Therefore, the ratio of the shear strength of undisturbed soil to that of remoulded soil is known as sensitivity, and it is an important parameter in geotechnical engineering for assessing soil stability and behavior.