The correct answer is:
B.) He could seek training to become a knight in the military
Step-by-step explanation:
In the system of primogeniture, the oldest son receives from the parents (that is, usually the father). That means that other sons have to look for "luck" in other places. This normally meant being accepted to be a knight (and hope to start a new family line) or, more infrequently, converting a priest and begging for a career in the church.