Answer:
The most reasonable inference is "Companies manufactured contact lenses from plastic because it was much cheaper".
Step-by-step explanation:
Based on the information provided, the manufacture of contact lenses from plastic started in the year 1940s.
Until 1940s, plastic was very difficult for companies to find. That means, there was no manufactured plastic lenses before that time.
Since 1940s. plastic lenses have become very popular.
Therefore, the reasonable inference is "Companies manufactured contact lenses from plastic because it was much cheaper".