Final answer:
In the Carboniferous period, forests of ferns and other seedless plants(B) such as club mosses and horsetails contributed to the formation of coal deposits.
Step-by-step explanation:
During the Carboniferous period, forests consisting mainly of ferns and other seedless plants(B) produced vast quantities of organic matter, which was buried and later became coal. These forests were predominantly composed of club mosses, horsetails, and tree-like ferns that flourished in the swampy forests. While gymnosperms were present towards the end of the Carboniferous period, they were not the primary contributors to coal formation.