examples of pure substance

Question

Which of the following are pure substances

1. Steam and water mixture in a container

2. Atmospheric air

3. Air and liquid air in a container

4. Gaseous combustion products

(a) 1,2 and 3     (b) 2, 3 and 4      (c) 1, 3 and 4    (d) 1, 2 and 4