Potential consumers experience a series of stages beginning with learning about a new product, trying it, and deciding whether or not to purchase it regularly. these series of stages are known as the (points :
2.
adoption process
product breakdown structure
market proliferation model
consumer product life cycle

These series of stages are known as the adoption process. Normally when a product comes into the market the customer does not jump to it the first time. Firstly the customer is always hesitant to go for the new product. They try to learn in details everything about the product. After learning about the product the customers give it a try to compare it with the product they were using before. Then only the customer decides whether or not to purchase the product, if it is better than the product they were using previously.

The answer is lymph sinuses.

Bees shall never produce milk no matter what but this is a joke and the answer is a breast that produces milk.