While gutting a fish, nathan encountered an air-filled sac-like structure. what is the purpose of this structure in fish?

a.
it enables fish to breathe in water.
b.
it serves as a reserve space to store fat.
c.
it harbors bacteria that benefit the fish.
d.
it provides buoyancy to the fish.

1. seamount a raised footwall block between normal fault creates this 2. syncline break between rocks where a hanging wall rises relative to a footwall 3. hot spring on rolling hills, this a dip between hills 4. volcanic neck created when a block with hanging walls slips down between normal faults 5. caldera underwater volcano that never reaches above sea level 6. horst natural hot water on earth's surface containing many minerals 7. graben underwater volcano whose top is eroded flat by waves 8. crater less than a mile in diameter; looks like a bowl at the top of a volcano 9. guyot magma that filled the central vent that remains after the volcano has eroded 10. reverse fault over 1 mile in diameter; looks like a bowl over a volcano