Identify the sentence that correctly employs the past perfect continuous tense?

اس جملے کی شناخت کریں جو ماضی کے کامل مسلسل تناؤ کو صحیح طریقے سے استعمال کرتا ہے؟

She has been reading the book for two hours

She had been reading the book for two hours when I called

She was reading the book for two hours

She reads the book for two hours

The sentence that correctly employs the past perfect continuous tense is: "She had been reading the book for two hours when I called."