Organisms cluster around hydrothermal vents in the ocean floor.
Chimneys top some hydrothermal vents.
Organisms cluster around chimneys  in the ocean floor.
What do organisms cluster around in the ocean floor?

[1] kalenchoes
[2] ferns
[3] bacteria
[4] Chimneys
[5] an object
[6] alveoli
[7] graptolites
[8] allow growth