Corrected sentences:
- Marmots live in burrows.
- They warn each other of danger with loud whistles.
- They are not easy to catch.
These sentences were already mostly correct. A few simple notes:
- "They" refers to the marmots. Good pronoun use.
- "Each other" is correct; you could also say "one another."
- "It's not easy to catch them." is okay, but "They are not easy to catch." is a little clearer because the sentence starts with the marmots (they).
- "Whistles" is plural because marmots make loud whistles. Nice detail!
Kid-friendly version (short and simple):
- Marmots live in burrows. They use loud whistles to warn each other when there is danger. Marmots are hard to catch.