The correct answer is A.
An increase in demand is a situation where consumers are willing and able to buy more of a good or service at any given price. This can be caused by a number of factors, such as an increase in income, a decrease in the price of substitutes, or an increase in the perceived benefits of the good or service.
A shift in the demand curve to the right indicates that consumers are willing and able to buy more of the good or service at any given price. This can be caused by any of the factors that increase demand.
A movement along the demand curve indicates that consumers are buying more of the good or service because the price has decreased. This is not an increase in demand, but rather a change in the quantity demanded.
B, C, and D are all incorrect because they describe a movement along the demand curve, not a shift in the demand curve.