Are humans alone in the universe, or is intelligent life out there somewhere? Find out how people throughout the years have explored this age-old question. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1934.

From Egyptian pyramids to Mayan temples, from Roman statues to the English language, our world's greatest empires still influence us today. This reader examines the history and legacy of several of the most influential empires. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1869.

Cold places, cold-blooded animals, catching a cold, getting cold feet - how many ways are there to be cold? Word count: 1956.

Madagascar has unique wildlife, beautiful forests, and a booming tourism industry. Come explore this fascinating island! Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1796.

Doctors today don't use leeches. Long ago, there were no big drug companies. But acupuncture, an ancient practice, is still helping people. Follow how medicine has - and has not - changed over time. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 2011.

Everyone loves a good pizza! But where did pizza begin? Is it good for us? Learn all about one of our favorite foods. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1804.

It's snot easy to find a reader this entertaining! Learn about mucus in humans and animals, and even in the laws of our countries! Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1727.

Animals find many interesting and efficient ways of moving. This reader discusses how the creatures of our planet navigate the water, land, and air in unexpected and unique ways. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises.Word count: 1751.

Determining the greatest invention of all time invites the greatest debate. From the internet to antibiotics, this reader explores our most significant contributions to education, technology, medicine, and transportation. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1622.

Music has always been important to people - and some animals! Explore the many ways music affects us, from whale songs to Yo-Yo Ma. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 2088.

What does the word 'hot' mean? From the Sahara Desert to heatstroke, from temperature to emotions, learn how heat affects our world. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1881.

A triathlon is one of the most demanding races a person can undertake. This reader explores some of the most famous and extreme triathlons around the world, including the Ironman and the Ultraman, along with some amazing competitors. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1949.

Water is one of the most essential ingredients for life on Earth. This reader looks at water in all its forms - in the air, on the ground, in the oceans, in our pipes - and explains how water keeps our lives moving. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1881.

Penguins that exchange wedding rings? A fish that doesn't swim? Learn all about the bizarre and unexpected behavior of animals from around the world. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1993.

What are the odds that you will be struck by lightning? Attacked by a shark? Become a superstar? This reader analyzes the chances of the incredible. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 2014.

Learn what it's like to live in the tundra, beside ancient pyramids, or near the Great Barrier Reef! Explore the food, clothing, architecture, and wildlife of these three special places. Use the unique code inside the book to access the online reader, complete with videos and interactive exercises. Word count: 1866.