The correct answer is D. Mature Phase
Step-by-step explanation:
Most products go through four different phases, this includes the emerging phase, the growing phase, the mature phase, and the decline phase. In each of these phases, the product has a different impact on the general market.
In the case of the mature phase, this occurs once the product is established in the market, which means the product is known by many people and is considered as key or necessary. For example, nowadays smartphones are in the mature phase because these are an important part of the market or are key. Moreover, this phase occurs after the product grows in the market, and before it declines. Thus, a product is a key technology during the mature phase.