A、Its diameter is 20 meters. B、Its diameter is 30 meters. C、Its diameter is 40 meters. D、Its diameter is 50 meters. B由新闻开头可知，工程师

A giant balloon has been launched by National Aeronautics and Space Administration (NASA) to test the largest parachute  ever made. Engineers hope the 30-meter diameter parachute will be used one day to bring a flying saucer-type lander safely down on the surface of Mars. Peter Bows reports from Los Angeles. “NASA scientists had hoped the test would pave the way for astronauts eventually to land on Mars. It was designed to investigate how a large landing vehicle would slow down as it falls through the atmosphere at supersonic speeds. A helium-filled balloon carried a saucer-shaped test vehicle to a height of about 37 kilometers and a built-in rocket fired it a further 50 kilometers before the parachute was meant to slow its descent, but it only partially opened, leaving the capsule to go down into the Pacific Ocean.”
1. How big is the parachute?
2. What is the purpose of the test?