Answer:
A. A shift outward in the production possibilities curve of the United States
Step-by-step explanation:
The production possibilities curve is the curve that shows the combination of goods the given country is able to produce given the fixed amount of resources. For example, given the fixed amount of resources, if there are 2 products, apples and bananas. Every single point along the curve show the combination of these two. If the country want to produce more apples they have to reduce the numbers of bananas to allocate the resources that originally used for bananas to use for additional apples, since they have fixed amount of resources.
The entry of women into the workforce increase the resource of production due to the more available labors. Thus, the production possibilities curve will shift outward because they can produce more goods without trade off of any products.