Which of the Following Statements Is True

Which of the following statements is true?

A) Because total utility is constant along an indifference curve, the marginal rate of substitution is also constant.
B) If an indifference curve is convex, the marginal rate of substitution varies along the curve.
C) The slope of an indifference curve measures the consumer's marginal rate of substitution.
D) Both b) and c) are true.