The classification system for organisms has changed from seven levels to eight. this happened because scientific consensus changed as scientists learned more about organisms. scientists did not test the seven-level system often enough to lead to consensus. the eight-level system of classification is an emerging idea that needs more testing. the seven-level system of classification was not supported by scientists.

Option A, scientific consensus changed as scientists learned more about organisms.

Explanation:

With the advancement in technology and further advent of DNA technology scientist were able to categories plan and animals more specifically based on their anatomy, physical and biological characteristics and DNA structure and type.  Until the DNA technology came into force and practical application, plants and animals were classified on the basis of seven categories i.e kingdom, phylum, class, order, family genus and species.The latest addition is of domain and that too was placed above the kingdom in hierarchy.

Hence, option A is correct

the relative standard reduction potential of the half-cell in which reduction occurs; more positive than the other half-cell. reduction is a chemical process in which electrons are added to an atom or an ion; it always occurs accompanied by oxidation of the reducing agent.

you can have just about every answer you can think of