The main characteristic of web 2.0 applications is they have the ability to become better the more that people use it which means that the answer to this is letter A. Web 2.0 usually collect data depending on what people do. The more data that they are able to get, the more that they can formulate the next actions that they will provide.
Web 2.0 applications will usually become more interactive as compared to the Web 2.1 applications. A lot of social media sites are already using web 2.0. This explains why there is always changing in order to accommodate the needs of people and what they want the application to offer to them.