Completar frases C22U4LA GE1Versión en línea Complete the time expressions with by or within. Use the future prefect for the verbs in parenthesis. por Modern English 1 the time our children reach adulthood , hundreds of species ( disappear ) off the planet . One study estimated that 2050 , 37 percent of terrestrial species ( die out ) or will be in danger of extinction . That is well over the next 30 years . Sea life is also in danger . the time that sea levels rise 50 centimeters ( about 20 inches ) , one - third of nesting beaches in the Caribbean ( lose ) , leading to the decline in turtle populations . By the end of this century , it is believed that seawater temperatures ( rise ) enough to affect the food supply of some oceans species . This impacts various species in different ways . For example , it is believed that only a few decades , the reproductive cycle of the sperm whale ( affect ) , which threatens the very survival of the whale itself .
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