People with blood type O are considered to be universal donors. That is, they can
donate blood to all other blood types. Using your knowledge of blood types and the immune
system, explain why this is true.

the law of original horizontality explains:   why rocks appear in layers. correct answer: b the law suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed.   the principle is used by geologists to make assumptions about the relative ages of sedimentary rocks.