An example of a pioneer species is a- a sparrowb- a lichen c- an earthwormd- a spider

The right answer is Lichen.

In ecology, a pioneer species is one of the first forms of life that colonize or recolonize a given ecological area.

Lichens are composite organisms resulting from a symbiosis between at least one heterotrophic fungus called mycobionte, representing 90% of all, and microscopic cells with chlorophyll (green algae or cyanobacteria autotrophic for carbon) called "photobionts" .

the missing space is phylum