Answer:
Primary
Explanation:
Ecological succession is the gradual change in the structure of a community or ecosystem. There are two types namely: primary succession and secondary succession. In primary succession, the change starts with no presence of life i.e. on a barren piece of land or rock. The pioneer species are organisms that have the ability to survive on bare rocks e.g lichens.
In the image attached, the succession starts with a BARE ROCK, and the first pioneer species are lichens before gradually moving into a climax community. Hence, this is an example of primary succession. Note that, in secondary succession, there is presence of SOIL.
Ans.
A common ancestor of humans and fish denotes the most recent organism, from which both the humans and fish have been evolved. Humans and fishes are vertebrates, which possess spinal column or backbone. Along with this, human embryos also go through a stage, during which they have gill-slits like structures in their neck as present in fish embryos.
These structures do not found in mature humans like fishes, but they support the fact that the humans share a common ancestral organism with fish.
Thus, the correct answer is option D). both species have gill slits when they are embryos.
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