Task: Question Answering
Input (English): Context: Inventors are always looking for ways to make our lives easier, greener and a whole lot more fun. Take a look at the following breakthroughs in science and technology. What in the world will inventors dream up next? Superhero Suit Have you ever dreamed of becoming a superhero? Dream no more. There's a real Iron Man suit, XOS 2, which instantly transforms the person wearing it. The suit provides the power to lift 200 pounds with ease and break slabs of wood with a single karate chop. It was designed to help the military with heavy lifting. One person in the suit could do the work of three soldiers. Up, Up and Away! It took him 30 years to develop it, and now Glen Martin's invention is ready to take off. The Martin Jetpack allows its operator to fly 8,000 feet into the air. Unfortunately, you can't soar through the skies too long. The jetpack holds only 30 minutes' worth of fuel. The aircraft will sell for $100,000. Hardworking Robot The EMIEW2 robot is the perfect office helper. Need a document delivered? No problem! It can also guide visitors to their destinations. The three-foot-tall robot can identify different human voices and respond to commands. One day, it may serve as a receptionist or a security guard. Green Machine Say goodbye to gasoline! The AirPod car runs on air power. That means this car won't pollute the environment. A high-pressure air tank can fill the car in minutes. The three-wheeler can travel about 130 miles between fill-ups. Beef Power All aboard the beef train! Amtrak's Heartland Flyer runs partly on fuel that is made from cow fat. The goal is to reduce carbon emissions by 10%. The train travels between Oklahoma City, Oklahoma, and Fort Worth, Texas. Robo-Guard EMILY is a robotic, four-foot-long buoy . She can swim through riptides at up to 24 miles per hour. Her inventor, Tony Mulligan, says that's 15 times as fast as human lifeguards! EMILY is powered by a tiny electric pump and operated by remote control. 
 Question: How many environment-friendly inventions are mentioned in the passage?
Output (English): three.