It is an aerial performance far beyond the capabilities of even the most complex modern aircraft: landing upside down on a ceiling. But it is routine business for bats, and now scientists have learned precisely how they do it. Brown University scientists observed two species: Seba's short-tailed bat and the lesser dog-faced fruit bat. They tracked their motions using three high-speed video cameras taking images at 1,000 frames per second, and studied weight distribution in the bats' body and wings. They found that by flapping both wings while folding one of them just a bit toward their body, a bat can shift its centre of mass to perform a midair flip in order to land on a ceiling. "Flying animals all move skillfully constantly as they fly through a three-dimensional environment," Brown biology and engineering professor Sharon Swartz said. "Bats employ this specific technique every time they land, because for a bat, landing requires reorienting from head forward, back up, belly down, to head down, toes up." When approaching their touchdown spot, bats are not flying very quickly, making it difficult to gather the type of aerodynamic forces produced by pushing against the air that could help position them for an upside-down landing. But their heavy wings enable them instead to create inertial  forces to adjust themselves in midair. Swartz said bats, as nocturnal  animals, are generally not fully appreciated as skilled pilots. "People have many opportunities to observe birds and insects flying, but the bat world is hidden in the night. The more we observe flight behavior in bats, the more we are impressed," Swartz said. Why aren't bats generally recognized as skilled pilots?
Their flying skills are controversial. Their flight behavior is hard to understand. They're not the most skilled in flying. They're primarily active at night.
Question: It is an aerial performance far beyond the capabilities of even the most complex modern aircraft: landing upside down on a ceiling. But it is routine business for bats, and now scientists have learned precisely how they do it. Brown University scientists observed two species: Seba's short-tailed bat and the lesser dog-faced fruit bat. They tracked their motions using three high-speed video cameras taking images at 1,000 frames per second, and studied weight distribution in the bats' body and wings. They found that by flapping both wings while folding one of them just a bit toward their body, a bat can shift its centre of mass to perform a midair flip in order to land on a ceiling. "Flying animals all move skillfully constantly as they fly through a three-dimensional environment," Brown biology and engineering professor Sharon Swartz said. "Bats employ this specific technique every time they land, because for a bat, landing requires reorienting from head forward, back up, belly down, to head down, toes up." When approaching their touchdown spot, bats are not flying very quickly, making it difficult to gather the type of aerodynamic forces produced by pushing against the air that could help position them for an upside-down landing. But their heavy wings enable them instead to create inertial  forces to adjust themselves in midair. Swartz said bats, as nocturnal  animals, are generally not fully appreciated as skilled pilots. "People have many opportunities to observe birds and insects flying, but the bat world is hidden in the night. The more we observe flight behavior in bats, the more we are impressed," Swartz said. Why aren't bats generally recognized as skilled pilots?
A. Their flying skills are controversial.
B. Their flight behavior is hard to understand.
C. They're not the most skilled in flying.
D. They're primarily active at night.
Answer: