'volatile' vs 'illusory'

[Ilovepsycho]

Q. Though scientific discoveries are often disproved shortly after they've been accepted as fact, scientists still seem to leap to hasty conclusions, demonstrating that the __________ nature of what can be called 'fact' has not eroded their confidence.

a. volatile

b. illusory

c. predictable

d. undeniable

I think 'volatile' and 'illusory' is both correct. What do you think of it?

[Gray]

I would say -- volatile. Because the previous sentence says that the so called facts are often disproved shortly, it means they are liable to lead to sudden change.
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First lesson - English, not english. I, not i. ~A student of English