Clostridium botulinum is a Gram-positive, obligate anaerobic bacterium that can form highly resistant endospores. Which characteristic of these endospores most directly contributes to their ability to survive harsh environmental conditions such as high heat and desiccation?

A thick protective coat containing keratin-like proteins that protects cellular components

A high concentration of ribosomes that allows rapid protein synthesis during stress

An increased number of plasmids that store stress-resistance genes

A flexible cell wall that expands to prevent structural damage