One gets it right they got brainliest
which geologic principle explains why the bottom stratum in a section of rock is the oldest?

cross-cutting relationships
superposition
unconformities
uniformitarianism

Superposition is the answer. The word has many meanings but in geology, it is when young rock forms on top of old rock. That means in a cross section of rock, the bottom stratum is the oldest.

answer; i believe the correct answer is ( proteins );

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: