Answer:
A- by reordering sentences to keep related ideas together.
The writer can best improve their organization by choosing option A, which involves reordering sentences to keep related ideas together. Currently, the paragraph jumps between discussing the differences between ponies and horses and their respective lifespans, which can be confusing for the reader. By grouping related ideas together, the paragraph will be more coherent and easier to follow. Option B, which suggests moving the first sentence to the end of the paragraph, does not address the underlying issue of disorganization and may make the paragraph less clear.