Which word is the maf'ul bihi in the new example حَفِظَتِ الطَّالِبَاتُ الدَّرْسَ?

Maf'ul Bihi: The Receiver of the Action

• حَفِظَتِ
• الطَّالِبَاتُ
• الدَّرْسَ
• the sentence has no object