Fact 1: Energy is used for heating a building by a heating system. Fact 2: Radiators are used to heat the building, The energy source is oil. Given the two facts above, what do radiators use to heat buildings?

Select from: (i) coal. (ii) CFCs. (iii) Solar power. (iv) Oil. (v) Oxygen. (vi) hot. (vii) Hydrogen. (viii) fuse.
Answer:
(iv)