Choose the underlined part among A, B, C or D that needs correcting

Choose the underlined part among A, B, C or D that needs correcting.
1. A warning sign ‘Overheat’ (A) may come on, (B) in the case turn off (C) the appliance (D) at once.
2. This is the car (A) which its engine (B) uses only 4 liters (C) of petrol (D) per 100 kilometers.
3. Kettledrums, (A) what were first (B) played on horseback, (C) were incorporated (D) into the orchestra
in the eighteenth century.