Final answer:
a. Thallophytes are the most primitive members of the plant kingdom. They are simple plants that haven't differentiated into stem, leaves, and roots. Bryophytes, Pteridophytes, and Gymnosperms display increasing complexity in comparison.
Step-by-step explanation:
The most primitive members of the plant kingdom are indeed A) Thallophytes. Thallophytes are algae and fungi, which are the most simple and earliest forms of plants. They are characterized by their plant body which does not differentiate into stem, leaves, and roots like higher plants.
B) Bryophytes are slightly more advanced than Thallophytes and include mosses and liverworts. C) Pteridophytes are even more advanced, developing vascular tissue for water and nutrient transport, and D) Gymnosperms are seed-producing plants, marking a significant step forward in plant evolution.
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