Final answer:
The central star of a planetary nebula is a small, hot, very dense white dwarf star that emits light due to internal heat and shapes the surrounding nebula.
Step-by-step explanation:
The "star" that is seen at the center of a planetary nebula is A) a small, hot, and very dense white dwarf star. Planetary nebulae are shells of gas ejected and expanding away from an extremely hot low-mass star that is nearing the end of its life. The appearance of planetary nebulae can vary greatly, looking like simple rings or more complex structures, depending on the angle we view them from. The shapes of these nebulae are also influenced by the stellar winds and radiation from the hot central star. Over time, a white dwarf will radiate away all its heat and eventually become a black dwarf, long after it has ceased to emit light.