This question examines the use of subordinate clauses. The correct answer is A because 'when she is hungry' is a subordinate clause that correctly describes the condition under which she goes to school. Option B is incorrect because 'because she eats' does not logically explain why she goes to school. Option C is incorrect because 'while eating' is a phrase, not a clause. Option D is incorrect because 'after she will eat' uses future tense in a subordinate clause, which is not correct.