The correct answer is B. Feature F1 is an example of an ordinal variable.
An ordinal variable is a variable that has a natural order, but the difference between two values does not have a meaningful interpretation. In the case of Feature F1, the grades A, B, C, D, E, and F have a natural order, but the difference between two grades does not have a meaningful interpretation. For example, a student who receives an A is not necessarily twice as good as a student who receives a B.
A nominal variable is a variable that has no natural order. For example, the variable “gender” is a nominal variable. The values “male” and “female” do not have a natural order.
It doesn’t belong to any of the above category is not a correct answer because Feature F1 is clearly an ordinal variable.
Both of these is not a correct answer because Feature F1 is an ordinal variable, not a nominal variable.