Refer to the Following Graph

Multiple Choice

Refer to the following graph:
The price of X is $20 and the price of Y is $40.

-At point B,

A) if the consumer obtains one more unit of Y, ½ unit of X must be foregone in order to keep utility unchanged.
B) if the consumer obtains one more unit of X, two units of Y must be foregone in order to keep utility unchanged.
C) the marginal rate of substitution is ½.
D) both a and c
E) all of the above