These two organisms may have evolved by coevolution. The last option in the given question is the correct option. The Latin-American humming birds had to evolve as per their surroundings, otherwise they would have become extinct in that region. For that sole purpose they had to have the long and curved bills. The flowers needed the humming birds for their pollination. To attach with the legs of the humming birds in the region, the flowers had to become sharply curved. The humming birds had to come in contact with the flower while sucking the nectar. this helped the plants in their pollination process. so both became mutually beneficial to each other.
These fossils are very useful for us because we can use them to date the layers of rock that they are found in. Fossils that can be used in this way are called index fossils, and rock layers with the same index fossils in them can be correlated. Not my answer, link here for full
http://peter-mulroy.squarespace.com/correlating-rock-layers/
I'm pretty sure its c or d
Parietal cells within the stomach lining secrete hydrochloric acid that lowers the pH of the stomach. A low pH (1.5 to 2) activates pepsin. Acetylcholine, gastrin, and histamine stimulate the proton pump in parietal cells to release hydrogen ions and decrease pH.
