[Solved] Which event marks the beginning of a supernova? A)the onset of helium burning after a helium flash in a star with mass comparable to that of the Sun B)the sudden outpouring of X-rays from a newly formed accretion disk C)the sudden collapse of an iron core into a compact ball of neutrons D)the beginning of neon burning in an extremely massive star E)the expansion of a low-mass star into a red giant Digestive Tube: A continuous hollow tube extending from the mouth to the anus, through which food is processed and nutrients absorbed. Plankton: Free-floating, mainly microscopic aquatic organisms found in the upper layers of the water; consisting of phytoplankton and zooplankton. Compare with nekton. Microscopic Organisms: Organisms too small to be seen with the naked eye, often including bacteria, archaea, some fungi, and protists. Anus: The distal end and outlet of the digestive tract.