instruction:
In this task, you need to write a topic word from the given fact. The topic word must have at least one word overlap with the given fact. The topic word often involves adding a new word from a related concept. In your topic word, use at least one word from the given fact. Topic words with two or more words work best.
question:
Fact: Mollusks are invertebrates such as the common snail.
answer:
common snail garden shell.


question:
Fact: contact between rocks over long periods of time causes rocks to smooth.
answer:
Rocks are formed.


question:
Fact: vein deposits of gold and silver are formed by igneous intrusion.
answer:

gold and silver are valuable.