To avoid mass extinctions of plants and animals， governments should protect a third of the oceans and land by 2030 and half by 2050， with a focus on areas of high biodiversity． So say leading biologists in an editorial in the journal Science．
This isn't just about saving biodiverse areas， says Jonathan Baillie of the National Geographic Society，one of the authors． It is also about saving ourselves by protecting   721    natural systems， or ecosystems，and their benefits to us， known as ecosystem services． "We are learning that the large areas that remain are important for providing services for all life． The forests， for example， are   722    for absorbing and storing carbon，" says Baillie．
At present， just 3.6 per cent of the planet's oceans and 14.7 per cent of land is protected by law． At the 2010 Nagoya Conference of the Convention on Biological Diversity， governments agreed to protect 10 per cent of the oceans and 17 per cent of land by 2020．
But this isn't nearly enough， says Baillie． In the editorial， he and his coauthor， Ya﹣Ping Zhang of the Chinese Academy of Sciences， want governments to set much bigger   723    at the next major conference on biodiversity in 2020．
"We have to enormously   724    our ambition if we want to avoid an extinction crisis and if we want to maintain the ecosystem services that we   725    benefit from，" says Baillie． "The trends are in a   726   direction， it's just we have to move much faster．"
It is hard to work out how much space is needed to preserve biodiversity and ecosystem   727   ， the pair say， because there is so much we don't know about life on Earth ﹣ like how many species there are．
   728   ，  most estimates suggest that between 25 and 75 percent of high biodiversity regions or major ecosystems should be protected．Therefore，we， including governments，should be   729     when setting goals and strategies．
"There is no doubt that we need far more land and sea   730    for conserving and retaining nature，"says James Watson at the University of Queensland in Australia． "Targets like 50 per cent are in the right ball park when it comes to the minimal   731    of area needed to conserve biodiversity．"
But Watson and others stress that which areas get protected is even more important than the overall percentage． "The key thing is to protect the right areas，" says Jose Montoya of the Station for Theoretical and Experimental Ecology in Moulis， France． "If we   732    protect a proportion of the territory，governments will likely protect what's easy， and that's usually areas of   733    biodiversity and ecosystem service provision．"
In fact， a third of the 3.6 percent of land that is already meant to be protected is actually being   734   ，Watson's team reported last month． So only   735    areas to be protected isn't enough．
721．A．stricter   B．wider        C．safer        D．simpler
722．A．unique     B．sufficient     C．critical      D．fit
723．A．examples    B．values       C．awards      D．objectives
724．A．increase     B．achieve      C．lack         D．frustrate
725．A．barely     B．currently     C．roughly      D．thoroughly
726．A．opposite     B．fixed         C．complex    D．positive
727．A．approaches    B．management C．benefits     D．degradation
728．A．Therefore    B．Furthermore   C．However    D．Otherwise
729．A．concerned    B．changeable    C．firm       D．cautious
730．A．deserted     B．secured       C．measured    D．distributed
731．A．damage     B．cost          C．amount     D．standard
732．A．completely    B．merely      C．virtually     D．desperately
733．A．mass        B．tropical      C．marine      D．low
734．A．exploited     B．expanded    C．restored     D．discovered
735．A．developing    B．covering    C．declaring    D．utilizing
【答案】721~725.BCDAB         726~730.DBCAB         731~735.CBDAC