51:09 An object is placed at 0 on a number line. It moves 3 units to the right, then 4 units to the left, and then 6 units to
the right. What is the displacement of the object?

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:

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

and after water is usually warmed by the sun the water temperature raises and then evaporates .