What Was a Critique of Klaus and Kennell's (1970s) Study

What was a critique of Klaus and Kennell's (1970s) study on mother-infant bonding?

A) Mothers could request which group they wished to participate in (extended versus limited contact) , biasing the samples.
B) Coerced and extended separation from their babies caused many mothers to suffer significant emotional distress.
C) Mothers with extended contact were also more likely to breast feed their babies, but the benefits of breast milk were unaccounted for.
D) The benefits of extended contact were not separated from the benefits of additional hospital staff support.