【T14】 A. BETWEEN B. IMITATE C. ACCELERATE D. OTHERWISE PHRASES: A. ENABLING THE BIRD TO【T13】______ B. IT【T14】______ COULD C. WOULD BE DIFFICULT TO【T15】______ D. FROM【T16】______ ITS FEATHERS THE EMPEROR PENGUIN TRAPS AIR IN ITS FEATHERS. NOT ONLY DOES THIS INSULATE THE BIRD AGAINST EXTREME COLD BUT IT ALSO ENABLES IT TO MOVE TWO OR THREE TIMES FASTER THAN【T17】______ HOW? MARINE BIOLOGISTS HAVE SUGGESTED THAT IT DOES SO BY RELEASING TINY AIR BUBBLES【T18】______ . AS THESE BUBBLES ARE RELEASED, THEY REDUCE FRICTION ON THE SURFACE OF THE PENGUIN'S WINGS,【T19】______ . INTERESTINGLY, ENGINEERS HAVE BEEN STUDYING WAYS TO MAKE SHIPS GO FASTER BY USING BUBBLES TO REDUCE FRICTION AGAINST THEIR HULLS(船身). HOWEVER, RESEARCHERS ACKNOWLEDGE THAT FURTHER INVESTIGATION IS CHALLENGING BECAUSE 'THE COMPLEXITY OF PENGUIN'S WINGS【T20】______ '.