During the Carboniferous period, the dominant plants, which late formed the great coal beds, were mainly :

Options

A. giant lycopods, horsetails, and ferns
B. gymnosperms
C. tree lycopods and cycads
D. treelike early vascular seed plants

Explanation

**Step-by-Step Solution:**

1. **Understanding the Carboniferous Period**: The Carboniferous period occurred approximately 300 million years ago and is known for its vast coal deposits. The term "Carboniferous" itself means "carbon-bearing," indicating the period's significance in coal formation.

2. **Identifying Dominant Plant Groups**: During the Carboniferous period, the dominant plants included various groups of vascular plants. The most notable among these were:
- Giant Lycopods
- Horsetail Ferns
- Gymnosperms
- Other early vascular seed plants

3. **Role of Climate and Environment**: The climate during the Carboniferous was predominantly tropical, which supported the growth of large plant species. These plants thrived in lush, swampy environments, contributing organic matter to the soil.

4. **Formation of Coal**: The organic matter from these plants eventually underwent geological processes involving heat and pressure, leading to the formation of coal. This process took millions of years and was crucial for the development of the coal beds we find today.

5. **Conclusion**: The main plants that dominated the Carboniferous period and contributed to the formation of coal beds were primarily Giant Lycopods and Horsetail Ferns, along with other early vascular plants.

**Final Answer**: The dominant plants during the Carboniferous period that later formed the great coal beds were mainly Giant Lycopods and Horsetail Ferns.

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