user: Why do we say tip of the iceberg?

assistant: Majority of Icebergs size/mass tends to be submerged under water. So, their size is misleading when seen from above surface. 
So the expression tip of the iceberg refers to a big issue when we see only a small part of it.

user: Tell me which of the following items are trees and which ones are weeds: aspen, ash, chickweed, crabgrass, oak, almond, dandelion

assistant: tree: aspen, ash, oak, almond
weed: chickweed, crabgrass, dandelion

user: What is Nevada City known for?

assistant: Nevada City is a town in Northern California that was famous during the California Gold Rush that was first settled in 1849.