Question

they stop succession from continuing
they help create conditions for other organisms to survive
they only live in climax communities
what is a climax community?
the first stage of succession
a community that cannot change
a stable ecosystem reached after succession
an ecosystem with no living organisms

Explanation:

Question 1 (about the role of certain organisms, likely pioneer species)

Pioneer species (implied by the context of succession) help create conditions (like soil formation, nutrient cycling) that allow other, more complex organisms to establish. The first option is wrong (they start succession, don't stop it), and the third is wrong (they are in early succession, not climax communities).

Climax community is the stable, final stage of ecological succession, where the ecosystem is in equilibrium. The first option is wrong (first stage is pioneer, not climax). The second is wrong (ecosystems can still change, though slowly). The fourth is wrong (it has living organisms).

Answer:

They help create conditions for other organisms to survive

Question 2 (What is a climax community?)