1. Suppose you wish to use number of "likes" for a video to predict the number of comments (assume that the comment section is open to any viewer).

what is the explanatory variable?

2. A researcher teaches a biology class in a university with 350 students. He sent out a survey to gather data for one of his recent research focusing on adults negative emotions in relation to exams. Extra class credits were provided to encourage students to complete the survey.

Is this a convenient sample?