Development of multicellular organisms probably began with the formation of
a. bacteria.
b. colonies.
c. microspheres.
d. oxygen.

B. colonies

Two distinctive organisms exist within the biosphere, the prokaryotes and the eukaryotes. The prokaryotes are called the unicellular organisms which in essence only have one cell. While the eukaryotes are called the multicellular organisms which have more than a cell.
These multicellular organisms like humans were first to create colonies or a community of the specie in order to have a better chance of survival.

They formed the oceans.  as they melted water was formed and the water made the oceans