A group of strict vegetarians have formed an association called Proveg. They protested recently against a famous and popular manufacturer on the issues of a chemical additive that goes into his toothpaste. The additive is dicalcium phosphate, and apparently the company obtains it from animal bones. Let me hasten to point out that I respect the right of this group to adopt and to propagate vegetarianism. I can also understand their sensibilities regarding animal bones. But, I am afraid, their concern may be misplaced. What they need to be reassured about is that the dicalcium phosphate is free of any organic contaminant from animal tissues. If the manufacturer proves that this phosphate is pure, the matter should rest there. If, on the other hand, tests reveal that the material is contaminated with any organic material from the animal, Proveg would be justified in their worries and protests.What is the critical completion of the passage?