When a Customer and a Supplier Choose To, or Are

When a customer and a supplier choose to, or are technically obliged to, integrate their processes,

A) there can no longer be a market operating between them for the item concerned.
B) there can be an adversarial relationship as each tries to gain advantage.
C) there can be strategic benefit, so long as the partners try to jointly maximise their profit in the downstream market.
D) all of the above.