TOEFL Reading: ETS-TOEFL阅读机经 - 9SF06VJ5SON5JQ5EL$

Which of the following can be inferred from paragraph 4 about the cave water and the calcium it contained in cave water? A. It made the cave water unsuitable for drinking. B. It was involved in combining paint pigments. C. It helped to bind paints to the surfaces being painted. D. It made paint last longer.