Answer:
Fossils closer to the surface are younger
Explanation:
It is called THERAPEUTIC INDEX. Therapeutic index is the comparison of the amount of a particular drug that causes the desired therapeutic effects and the amount that causes toxicity. The index can be low or high. A drug with a low therapeutic index will require only a small increase in dose to produce toxic effects in users.
The answer that best fits the blank provided above is C3a and C5a. Mast cells release this so called histamines once they are exposed to C3a and C5a which are fragments of complement proteins. These are also called as <span>Anaphylatoxins along with C4a. Hope this helps.</span>
"What is human nature?" is the key question psycology seeks to answer