Sitting in a Hot Tub with Water at 100°F Feels

Sitting in a hot tub with water at 100°F feels much hotter than standing outside in 100°F air on a hot day.This analogy illustrates why

A) interstellar dust is dark at optical wavelengths but bright in the infrared.
B) supernovae can heat their shells to such high temperatures.
C) an astronaut would not burn up while floating in 10⁶ K intercloud gas.
D) the Solar System is immersed in a hot bubble of gas.
E) fusion occurs only in the cores of stars.