Xinyi asks John why carbon monoxide is so dangerous. He replies it's because it affects the blood. Which statement best explains how CO harms the body?

Xinyi and John study the carbon cycle. Which step directly removes carbon dioxide from the atmosphere?

While working on their smog awareness project, Xinyi explains the role of unburnt hydrocarbons and ozone. Which condition is necessary for photochemical smog to form?

John asked Xinyi, “What’s the main gas in the air?” What is the correct composition of clean, dry air at sea level?

Xinyi saw a poster showing carbon monoxide and asked John, “Where does it come from?” Which is a common source of carbon monoxide in urban areas?

John and Xinyi read about the ozone layer in class. Why is the ozone layer important for life on Earth?

Xinyi asked John why sulfur dioxide is harmful. What is a harmful effect of sulfur dioxide?

John read that global warming is linked to greenhouse gases. Which pair of gases is mainly responsible for the greenhouse effect?

Xinyi wondered why plants are called “carbon sinks.” Which process in the carbon cycle reduces the greenhouse effect?