I'm taking a test and have to guess the right answer to the question after the article. Article: Humans might be the most highly-evolved species on the planet, but most animals possess skills we can only dream of having. Imagine how much electricity we could save if we could see in the dark the way cats do. Imagine leaping from tree to tree like a monkey. Giraffes, which are otherwise calm and good-natured, sleep only 4.6 hours a day. We realized a long, long time ago that nature provides the best blueprint for invention. We've borrowed canals from beavers and reflectors from cat's eyes. Although the words "bionics" became popular only after the 1960s, history shows that nature has always provided ideas on solving everyday problems. Our archives don't go back to the time of Leonardo da Vinci and his bird-like flying machines, but we can take you to the late 19th century, where we applied those same principles for building our first practical airplanes. To prepare for their flight at Kitty Hawk, the Wright brothers studied the movements of pigeons to figure out how they stayed high up when they were heavier than air. Their success inspired scores of successors to improve on the airplane by studying various aspects of nature. One of Orville Wright's pupils caught and stuffed seagulls to examine their wingspan. Meanwhile, two French inventors examined spinning sycamore seeds in an effort to apply those same motions, reversed, to a helicopter . Some examples are more obvious than others. The outside of the airplane designed by the Wright brothers looks like a minimalistic structure. On the other hand, Barney Connett's fish submarine actually looks like a fish. Some bio-inspired concepts have yet to be invented. In the 1960s, the US Army commissioned several university professors to conduct research on the motor skills animals in hope of applying those same abilities to tanks. Tanks that run like horses or jump like grasshoppers -sounds shocking, doesn't it? But imagine how life would change if we could achieve that. Question: Which of the following is true about the research carried out by the US Army? Options: A: It has cost a large sum of money. B: It has changed our life. C: It has improved the abilities of tanks D: It has not succeeded yet.
The answer to this question is:
D