Answer:
B) The partner will need to create a one-way outgoing trust in the external domain.
Step-by-step explanation:
In a one-way trust, the domain who is trusting other domain makes its resources available to the domain who is trusted. With right permissions a user from the trusted domain can have access to the resources of the trusting domain.But the user in trusting domain cannot access resources of the trusted domain.
So to complete the trust the partner needs to create a one-way outgoing trust.