Read the following passage: "The process of vulcanization, discovered by Charles Goodyear in the mid-19th century, transformed rubber from a sticky, brittle, and temperature-sensitive material into a durable, elastic, and more resilient product. Before vulcanization, natural rubber would soften in heat and harden in cold, making it impractical for many applications. Goodyear's accidental discovery involved heating rubber with sulfur, which forms cross-links between the polymer chains. These cross-links greatly increase the material's strength, elasticity, and resistance to chemical degradation and temperature changes. This breakthrough paved the way for the widespread use of rubber in tires, industrial products, and countless consumer goods, fundamentally impacting transportation and manufacturing." What was the primary problem with natural rubber that vulcanization addressed?

1. AIts inability to be molded into shapes.
2. BIts instability and temperature sensitivity.
3. CIts high cost of production.
4. DIts excessive hardness and rigidity.