A Type Ia Supernova Involves the Transfer of Mass from One

A type Ia supernova involves the transfer of mass from one star to a companion white dwarf? Yet, in some cases, astronomers cannot locate a star near where they see Type Ia explosions. How do they explain the absence of a companion star?

A) they suggest that the companion star is a black hole
B) they suggest that the companion star is always of such low mass, it's easy to miss
C) they suggest that some type Ia supernova are caused by the collision of two white dwarfs, both of which then explode
D) they suggest that some type Ia supernova explosions come from a single massive star where the fusion of iron causes a catastrophe and great release of neutrinos
E) no one has any idea how to explain type Ia supernovae which do not leave behind a companion star; it's an unsolved mystery