What best describes the function of a Unary Constraint in CSPs$?$

Select one:

Limits the possible values that can be assigned to a single variable.

Dictates the relationship between pairs of variables in a set.

Ensures that all variables within a specified set meet an aggregate condition, such as a sum or product.

Requires that all variables in a set must take unique values.

Enforces that variables must alternate between numerical values in a specific sequence.