What Is a "Downside" of Referrals as a Source of Recruits

Multiple Choice

What is a "downside" of referrals as a source of recruits?

A) They limit the likelihood of exposing the organization to fresh viewpoints.
B) Referrals may contribute to hiring practices that appear unfair e.g.nepotism.
C) Using referrals is much more expensive than most other recruiting sources.
D) The recruitment process becomes more complex.
E) "a" and "b."