The correct answer is C) an agreement with local native Americans.
The factor in Pilgrim's success in their new colony was an agreement with local native Americans.
The Mayflower ship arrived at the coast of Massachusetts with 41 Pilgrims, among other English, in September 1620. Specifically, they arrived at Cape Cod. They established at Plymouth Rock where they suffered a terrible winter. The Pilgrims that survived established peace treaties with the Native American tribes that were already in those territories. This allowed the Pilgrims to have good relations and trade with the tribes in the following years.
The other options of the question were a) overcame a weak leadership from their governor, b) quick military victory over tribes, and d) early planning kept most Pilgrims alive after the first winter.