6. As a statistician, one of your key responsibilities is to figure out strong factors for your linear regression model. More specifically, you need to find what kind of independent variables you need to use so that your linear regression model can have a better prediction for your dependent variable, y. Suppose you are working on a subscription product (such as newspaper, magazine and blog). You want to find out how to increase the number of subscribers in the future. Note that the number of subscribers in the future can include keep current subscribers and attract new subscribers. For example, topic of an article can be a good variable because an article with an attractive topic can help attract more new subscribers. Therefore, we can put topic of an article into the linear regression model. List five or more independent variables you think to be possible