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.If Charlie is consuming 40 apples and 160 bananas, then 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) -4.
B) -8.
C) -41.
D) -1/4.
E) -1/8.