Step 1: Sort each company by who owns it.
ONGC is run by the government, so it belongs to the public sector; Airtel is privately owned, so it belongs to the private sector.
Step 2: Place the remaining two.
Maruti Suzuki is jointly held by the government and a private partner, making it the joint sector example, while Amul is run by its member farmers, making it the cooperative sector example.
Step 3: Line up the matches.
This gives public to ONGC, private to Airtel, joint to Maruti and cooperative to Amul, exactly as listed under option C.
Step 4: Final answer.
The correct option is (C).