If Goods X and Y Are Substitute Goods,then a Decrease

If goods X and Y are substitute goods,then a decrease in the price of Y,other things constant,

A) has no real effect on the quantity demanded of good Y,but increases the demand for X.
B) results in an increase in the quantity of Y demanded and a decrease in the demand for X.
C) results in a decrease in the amounts of both X and Y demanded.
D) increases the quantity of Y demanded,but has no effect on the amount of X demanded.