In this problem we have that
Let
x ------>number of books
y ----> the total cost
we have the ordered pairs
(1,5), (2,6), (3,8( and (4,12)
so
Verify each statement
Option A is not true
The domain is the set (1,2,3,4)
Option B
The range is the set (5,6,8,12)
so
the option B is true
Option C
The relation is a function, because for one value of x there is only one value of y
so
Option C is true
Option D
we have that
The cost is the dependent variable and the number of books is the independent variable
so
option D is not true