What is an outcome of lack of oxygen?

Brain cells are very sensitive to a lack of oxygen. Some brain cells start dying less than 5 minutes after their oxygen supply disappears. As a result, brain hypoxia can rapidly cause severe brain damage or death.

Explanation:

Other symptoms can include: hallucinations and delusions; increased agitation and confusion; depression and other mood disorders; personality changes, such as irritability and a reduced threshold for frustration; and an inability to focus or concentrate.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.