In Lazzaro Spallanzani's experiments refuting abiogenesis with boiled broths sealed in flasks, what criticism did skeptics raise?

• A. The broths were contaminated prior to boiling.
• B. He failed entirely to use nutrient-rich media.
• C. He should have used open containers instead of sealing them.
• D. The prolonged boiling supposedly eradicated vital properties required for generating life.

Answer: (D)