911 - Logical Reasoning

Question: Using computer techniques, researchers analyze layers of paint that lie buried beneath the surface layers of old paintings. They claim, for example, that additional mountainous scenery once appeared in Leonardo da Vinci's Mona Lisa, which was later painted over. Skeptics reply to these claims, however, that X-ray examinations of the Mona Lisa do not show hidden mountains.
Which of the following, if true, would tend most to weaken the force of the skeptics' objections?

1. There is no written or anecdotal record that Leonardo da Vinci ever painted over major areas of his Mona Lisa.
2. Painters of da Vinci's time commonly created images of mountainous scenery in the backgrounds of portraits like the Mona Lisa
3. No one knows for certain what parts of the Mona Lisa may have been painted by da Vinci's assistants rather than by da Vinci himself.
4. Infrared photography of the Mona Lisa has revealed no trace of hidden mountainous scenery.
5. Analysis relying on X-rays only has the capacity to detect lead-based white pigments in layers of paint beneath a painting's surface layers.