Image is not provided in the question, so the image is attached below.
Answer:
Fewer plants
Step-by-step explanation:
The region X in Venn diagram represents fewer plants in the region.
As the regions marked X represents fast-flowing areas of rivers and streams which can be possible if the flow of water get less obstruction in its way, so if their will be fewer plants, river will get less resistance and can flow faster.
Other option do not affects the flow of water.
Hence, the correct option is fewer plants.