Charlie's Utility Function Is U(A, B)= AB, Where a and B

Multiple Choice

Charlie's utility function is U(A, B) = AB, where A and B are the numbers of apples and bananas, respectively, that he consumes.When Charlie is consuming 20 apples and 80 bananas, if we put apples on the horizontal axis and bananas on the vertical axis, the slope of his indifference curve at his current consumption is

A) -8.
B) -1/4.
C) -20.
D) -4.
E) -1/8.