The x-axis represents a student's age in years and the y-axis represents the number of times the student cried each month on average.

Based on the information provided and the typical characteristics of scatterplots that compare two variables, the three vocabulary words that can be used to describe the data represented in the scatterplot are:

1. Bivariate - This term applies because the scatterplot involves two variables: age and the average number of times a student cried.

2. Positive trend - This term would apply if as the student's age increases, the number of times they cried decreases or maintains a pattern (or vice versa, depending on the actual data trend).

3. Linear trend - This term could apply if the data points in the scatterplot form a straight-line pattern, indicating a consistent relationship between the age and the frequency of crying.

If you have specific characteristics from the scatterplot regarding the trend or relationship, you can adjust the choice of words accordingly, particularly regarding whether the trend is indeed positive or negative.