An academic definition has three compulsory components (1) a term to be defined; (2) the general class that the target term belongs to; (3) the differentiating features of the target term. Please identify to which categories the underlined part is in the following definitions.
Salinity is the amount of salt dissolved in a particular volume of water.
A、A term to be defined;
B、The general class that the target term belongs to;
C、Differentiating features of the target term;
D、/