Answer: Wheat production
Step-by-step explanation: In a perfectly competitive market structure, the number of market participants is very high and each entity in the market works at a small level.
In a perfectly competitive market no individual participant can influence the price and it is determined by the market forces of supply and demand.
From the characteristics explained above we can conclude that Wheat is the right option.
Other options like steel, airplane and electricity are examples of monopoly or oligopoly.