Which of the following are examples of broadleaf weeds that are winter annuals?

The identification of common chickweed and shepherd's purse as examples of broadleaf weeds that are winter annuals is accurate because both plants complete their life cycle within a single growing season and typically germinate in the fall, overwintering as seedlings. This enables them to establish early in spring, produce flowers, and set seeds before dying off with the summer heat.

Winter annuals like common chickweed and shepherd's purse are specifically adapted to take advantage of the cooler growing conditions of fall and spring, which gives them a competitive edge over other weeds and plants that thrive in warmer temperatures.

In contrast, the other plants mentioned in the other choices do not fall into the winter annual category. Dandelion and plantain, while broadleaf weeds, have different growth cycles and can be perennial. Crabgrass and goosegrass are warm-season annual grasses, and yellow foxtail and barnyard grass also belong to the warm-season category. This distinction between warm and cool-season growth habits is essential in understanding weed management strategies in turf and ornamental settings.