Final answer:
In stem-changing verbs with two 'e's, the second 'e' in the stem changes, as seen in verbs like 'entender' where 'entend-' changes to 'entiend-'.
Step-by-step explanation:
In the case of stem-changing verbs in Spanish, when you have a verb with two 'e's, the rule of thumb is that the second 'e' in the stem changes.
For instance, in the verb entender (to understand), the stem is entend-, and the second 'e' changes to 'ie' in most present tense forms (except nosotros and vosotros).
So, the correct answer is b) The second 'e'.
This follows the pattern seen in other stem-changing verbs such as preferir where the second 'e' changes to 'ie' (yo prefiero, tĂș prefieres, etc.).
However, always remember that these changes apply to the present tense and might not apply to other tenses like the preterite.