A) attempt B) cheaper C) classify D) coauthored E) come F) effort G) enable H) especially I) exactly J) identify K) obstacle L) small M) soaring N) well-being O) yet Researchers have identified 1.4 million animal species so far—and millions remain to be discovered, named, and scientifically described. So how much would it actually cost to __ _1__ _every animal on Earth? A pair of Brazilian scientists has crunched( 详细计算 )the numbers and __ _2__ _up with an answer: $ 263 billion. That's way more than the $ 5 billion that famed Harvard University biologist Edward O. Wilson estimated back in 2000—and that was for every species on Earth, not just animals. But even $ 263 billion would be a _ __3__ _ price to pay to understand the creatures that __ _4___ such essentials as agriculture, fisheries, new drugs, and energy sources, says ornithologist( 鸟类专家 )Joel Cracraft of the American Museum of Natural History in New York City. "Literally, the world economy runs on biodiversity," he says. "People don't understand really, deeply how much we depend on biodiversity." Most biologists agree that with extinction rates __ _5_ __and climate change looming, the __ _6_ __to document the planet's biodiversity—or biota( 生物区 )—is urgent, __ _7_ __considering the essential role these life forms play in crop pollination, clean air, and other aspects of human __ _8_ __"We are losing species by extinction faster than we are describing new species" according to some estimates, says biologist Antonio Marques, who __ _9__ _the new paper with Fernando Carbayo, both at the University of St. Paulo in Brazil. "We have to know the biota to preserve and conserve the biota," he says. Besides the money, another huge __ _10__ _to a complete understanding of the animal kingdom is a global shortage of taxonomists( 分类学家 ), experts say.