Which type of plant primarily reproduces with unprotected seeds?

The correct choice identifies gymnosperms as the type of plant that primarily reproduces with unprotected seeds. Gymnosperms are a group of seed-producing plants that do not enclose their seeds within an ovary or fruit, which is a defining characteristic of this group. Their seeds are often found on the scales of cones or exposed in some other manner, which differentiates them from angiosperms, where seeds are typically enclosed within a fruit.

In contrast, angiosperms produce flowers and fruits that contain their seeds, providing protection and facilitating dispersal. Cycads are a class within the gymnosperms, but they also possess the same unprotected seed characteristic as other gymnosperms. Herbaceous plants, on the other hand, refer to non-woody plants and can include members from both angiosperms and gymnosperms; however, they don't represent a separate group that exclusively reproduces with unprotected seeds. Thus, gymnosperms is the most accurate answer since they are the primary group that reproduces this way.