Match column I with column II and select correct option from given codes.

Column I	Column II
A. Pioneers	(i) Vegetation which modifies its own environment and thus causing its own replacement
B. Autogenic succession	(ii) Replacement of existing community by external conditions
C. Allogenic succession	(iii) Establishment of organisms in an area into which y have come by dispersal or migration
D. Ecesis	(iv) Primary colonizers

Pioneers or primary colonisers are the first organisms to inhabit an area. In ecology, autogenic succession is succession driven by the biotic components of an ecosystem whereas allogenic succession is succession driven by the abiotic components of ecosystem. In other words, we can say that, in autogenic succession, the vegetation(biotic components) itself modifies it own environment and causes the succession to occur. In allogenic succession, replacement or modification of existing community occurs by external(or abiotic) factors such as volcanic eruptions, flooding, human interference, etc. Ecesis refers to the establishment of organisms in a new environment or area, into which they have come by dispersal or migration.