Although Centuries Ago, Astronomers Thought That a Nova Was a New

Although centuries ago, astronomers thought that a nova was a new star, appearing for the first time in the heavens, today we know that it is:

A) a binary star system in which one star is a white dwarf and mass is being transferred to it
B) the explosion of a massive star when the fusion of iron leads to the collapse of its core
C) the brightening of a neutron star when it becomes a pulsar
D) the emission of a bright planetary nebula late in a star's life
E) the birth of a high-mass protostar in a giant molecular cloud