Smith and cuvier discovered that similar groups of fossils in distant rock layers could be correlated. why was this such a major breakthrough in geology?

a. it disproved the principle of superposition.
b. it proved igneous rocks held more information than sedimentary rocks.
c. fossils could now be used to identify rock layers.
d. fossils were no longer needed to study the history of earth.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

i'm assuming that it's c.) red bank..