Answer: c). The demand for Bluetooth headsets increases.
Explanation: Factory incentives on cell phones have encouraged consumers to upgrade their phones. The up-gradation of cell phones will encourage consumers to buy more Bluetooth headsets as they are now supportable with the cell phones. This will shift the demand for Bluetooth headsets to the right. As a result the price and quantity of Bluetooth headsets will increase. Thus, c is the correct option, demand for Bluetooth headsets increases.