A "stem-changing verb" in Spanish is a verb that undergoes a change in the stem (the part of the verb that remains after removing the -ar, -er, or -ir ending) when it is conjugated in certain forms. Typically, these changes occur in the present tense for all forms except for the nosotros and vosotros forms. Therefore, the most accurate definition in your options would be:
• a verb that has a change in both the beginning and ending parts of the word (although it's important to note that the change is primarily in the stem, not the beginning).
However, this option is not completely accurate either. A better definition would focus on the fact that the stem changes, but since that's not listed, the closest one regarding changes would be the second option.