A property can be measured or observed without matter changing to an entirely different substance.

1.chemical

2.physical

physical property is the property that can be observed without the matter under experiment undergo permanent changes it is reversible

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."