If the demand for a certain stock increases while at the same time the supply of the stock decreases, then: a) the quantity sold of this stock will increase, but the effect on its price can not be determined. b) the quantity sold of this stock will decrease, but the effect on its price can not be determined. c) the stock's price will fall, but the effect on the quantity sold cannot be determined. d) the stock's price will rise, but the effect on its quantity sold cannot be determined