Complete the sentence with the most suitable word from the list.
Finding enough food for the world’s growing population won’t be easy; it’ll be a big ...

• drain.
• powered.
• save.
• solution.
• challenge.
• produce.
• vertical.
• population.
• mankind.
• soared.
• wasteland.
• lush.
• consume.
• nutrients.
• structure.
• environmentally.
• wonders.
• convert.