How much oxygen does the brain need to stay "conscious"?

20% of the body's oxygen supply.

Explanation:

The brain represents just 2% of a person's body weight, yet it uses about 20% of the body's oxygen supply. Without it, the brain can't perform even the most basic functions. The brain relies on glucose to power the neurons that control everything from conscious functions like planning and thought to automatic, unconscious processes like managing heart rate and digestion.

An adults brain requires around 20% of the body's oxygen.

Explanation: Because the brain uses about 25 percent of your oxygen intake, supplying it with enough oxygen is essential. For people with chronic lung diseases, getting enough oxygen is difficult. When the brain doesn't receive the amount of oxygen it needs, cerebral hypoxia can occur.

the plates spread at mid-ocean ridges (they are divergent plate boundaries) which allows magma to rise through the weakness between the plates. the magma then emerges as lava from the boundary and cools, creating a new crust.

b and c would be the answers