An "increase in demand" means that:
a. the demand curve has shifted to the left.
b. price has declined and consumers, therefore, want to purchase more of the product.
c. given supply, the price of the product will decline.
d. the demand curve has shifted to the right.

d. the demand curve has shifted to the right.

Explanation:

An increase in demand is associated with a rightward shift of the demand curve.

A decrease in demand leads to a leftward shift of the demand curve.

Some of the factors that cause an increase in demand :

1. Increase in income if the good is a normal good.

2. Expectation of an increase in price in the future.

3. Increase in price of the substitute.

An increase in Quanitity demanded leads to an upward movement along the demand curve. Only changes in price leads to a movement along a demand curve.

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