Understanding the Sentence Structure
In the sentence "She (eat) her breakfast before going to school," we need to determine the correct form of the verb "eat" to maintain grammatical accuracy.

Analyzing the Options
- a) eat - This is the base form of the verb and is not suitable here, as the sentence requires a past action.
- b) ate - This is the past tense form of the verb "eat." It indicates that the action of eating breakfast happened before another action (going to school), making it a strong candidate.
- c) eats - This is the present simple form of the verb. It does not fit because the context suggests a completed action prior to another event.
- d) will eat - This is the future tense form. It implies that the action of eating breakfast will happen later, which contradicts the context of the sentence.

Conclusion
The correct choice is b) ate. The sentence should read: "She ate her breakfast before going to school." This construction clearly indicates that her breakfast was consumed before she left for school, adhering to the sequence of events in the past.

Key Points Recap
- Base form (eat): Not suitable for past context.
- Past tense (ate): Correct form for completed actions.
- Present simple (eats): Incorrect for past actions.
- Future tense (will eat): Conflicts with the context.
By selecting "ate," the sentence conveys a clear sequence of actions, essential for effective communication in English.