According to modern ideas, the first step in the origin of life was a. volcanic activity b. the formation of simple organic molecules c. the presence of oxygen in earth’s environment d. the evolution of autotrophic prokaryotes

I say the answer is letter B.
It is definitely not D.
A and C led to B, which is the first step of actual life.

A. Volcanic activity, while proposed as a source of energy and minerals for the abiotic assembly of chemical molecules and compounds necessary for the origin of life, are as potentially destructive as they are supportive.

b. The formation of simple organic molecules are possible within the limits of the geochemical environment and entropy, which limits what elements can combine to form potential biotic compounds. This includes amino acids, sugars, lipids and other simple molecules, none of which are the full base of necessary compounds for a living entity. The concept of chemical evolution, organic molecular evolution, abiogenesis, or biological evolution are mythological naturalistic hypotheses, not science.

c. The presence of oxygen in the Earth's environment relates to atmospheric oxygen, which was not present in any amount to impact the development of 
simple and complex molecules for the origin of life. Oxygen did not increase until the formation of bacteria that took in CO2 and expelled O2.

d. Autotrophic prokaryotes are arguably the simplest single cell organisms that were part of the first life.  "The evolution of" implies they are existing, as only living organisms can adapt. Any adaptation they may have experienced implies there was a prior form.

Consequently, volcanic activity, a.,  would predate the other 3 activities.