25. The students ........................... (study) hard because they wanted to pass the exam.
Для образования Past Continuous необходимо использовать вспомогательный глагол to be в форме прошедшего времени (was/were) и причастие настоящего времени (V-ing).
В данном предложении подлежащее The students, поэтому используем were.
The students were studying hard because they wanted to pass the exam.
Ответ: The students were studying hard because they wanted to pass the exam.