The correct option is B a
A variable is a symbol representing a quantity whose value is unknown.. Generally, we use a single letter to represent a variable.
5 is an integer, which has a fixed value. It cannot be used as a variable.
a can be used as a variable.
135 also has a fixed value, which cannot be used as a variable.
π is a constant that has a fixed value close to the value of 227. Hence it cannot be used as a variable.