While the colonists would eventually push westward, first, they were in for a long, difficult winter, and the main challenge was to _________ their existing resources.
The sentence states that while the colonists would eventually push westward, they had to first deal with the challenge of a long and difficult winter. And it had to do something with their existing resources. Clearly they have to
preserve the resources if they have to successfully push westward. Hence,
steward and
husband are the correct answers.
_________________