Succession occurs because
a. organisms gradually change the environment
b. climax communities are not possible
c. dominant organisms drive out pioneer species
d. ecosystems never reach a sustainable point

Correct A) Organisms gradually change the environment

Succession occurs when there is a disturbance in the environment, it would be a minor disturbance like a fire or a major disturbance like a volcanic eruption. Based on the disturbance, succession can be divided into two types:

1). Primary Succession: Primary succession is said to happen when a group of the species or a community evolve from a barren land or a land with no life. This land is fresh and does not have any life on it.

Example: Primary succession occurs after a volcanic eruption

2). Secondary Succession: The secondary succession is said to occur when there is a disturbance and it destroys ecosystem but still there is an availability of nutrient, seed, and soil.

Example: Forest Fire

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.