Step 1: List what Atterberg limits actually measure.
The liquid limit, plastic limit and shrinkage limit are all expressed as a percentage water content at which a fine grained soil changes its physical state, from liquid to plastic, from plastic to semi solid, and so on.
Step 2: Eliminate the unrelated soil properties.
Soil texture describes the fixed proportion of sand, silt and clay in a sample and does not change with water added later, so texture cannot be what these limits track. Soil structure refers to how particles are arranged into aggregates, and cohesion is a shear strength parameter, neither of which is defined purely by a water content boundary.
Step 3: Match the remaining option to the definition.
Since every one of the Atterberg limits is stated purely in terms of the moisture content at which behaviour changes, they are indices of soil moisture at critical consistency stages, not of texture, structure or cohesion directly.
\[ \boxed{\text{Soil moisture}} \]