n. 1,000
There are thousands of kinds of fish in the ocean.

n. 1,000,000
Almost 19 million people live in Delhi, India.

n. using or doing something helpful
When studying English, it is useful to have a dictionary.

n. a hard material that mountains and the Earth are made of
There are many rocks on the beach.

n. the empty place between planets and stars
An astronaut is a person who travels into space.

n. a deep hole dug by people in the ground
People mine resources like gold, diamonds, and other minerals.

n. digging deep into the earth to find useful materials
Mining is the industry and activities connected with getting valuable or useful minerals from the ground.

n. the planet where people live
Christopher Columbus believed that the Earth was round.

n. a strong metal commonly used for making all kinds of tools
Iron is used in making steel.

n. a soft, valuable metal often used for making rings, necklaces, etc.
Olympic athletes can win gold, silver, or bronze medals.