A) References cannot be null,every reference refers to some object, although it may or may not be valid.
B) Reference doesn't need an explicit dereferencing mechanism
C) Once a reference is created, it cannot be later made to reference another object.
D) They are entirely different concept. Pointer stores the address whereas Reference is an alias of some variable.
https://en.wikipedia.org/wiki/Reference_(C%2B%2B)