13. What does the "e" in the verb pensar change to in the "yo" form, since it is a stem-changing verb. (2 points)

In the verb "pensar," the "e" changes to "ie" in the "yo" form. Therefore, the correct answer is:

• it doesn't change.

In the "yo" form, "pensar" becomes "pienso." So, since you specifically asked about the "yo" form, it doesn’t retain the "e" in a direct way, but instead changes to "ie."