The correct answer is: A. an activity undertaken by a firm to increase demand.
Product variation is the process of offering different versions of a product to appeal to a wider range of customers. This can be done by changing the features, price, or packaging of the product. Product variation can help to increase demand by making the product more appealing to a wider range of customers.
Option B is incorrect because product variation is not a problem with quality control. Quality control is the process of ensuring that products meet certain standards of quality. Product variation is a deliberate attempt to make products different from each other.
Option C is incorrect because product variation is not an activity undertaken by a firm to make demand more price inelastic. Price elasticity of demand is a measure of how responsive demand is to changes in price. Product variation does not affect price elasticity of demand.
Option D is incorrect because product variation is an activity undertaken by a firm to increase demand.