Suppose the demand for good X is given by QdX. QdX equals to 10 plus a x PX plus b x PY plus c x M where x denotes the multiplication, PX is the price of good X, PY is the price of good Y, QdX is the quantity demanded for good X and M is the income. The multiplication has priority over addition. From the law of demand we know that a will be

Select one:

a.less than zero.

b.none of the statements associated with this question are correct.

c.zero.

d.greater than zero.