Bonjour,
Réponse :
1.Massive wildfires are a threat to nature: they burnt down 9.4 million acres of forests in the U.S. in 2015. But some insects can be even more damaging! The bark beetle has already destroyed .46 millions of acres of American forests.
burnt down : prétérit ( action datée, passée )
has been destroyed : présent perfect ( constat + adverbe de fréquence "already" )
2. Since its first "lights-out" event in 2007, Earth Hour has grown to engage more than 7,000 cities and towns worldwide.
has grown : présent perfect ( il y a une année, mais "since" nous indique qu'il s'agit d'un point de départ ... donc pas de prétérit )
3. Australia's natural wonder is in danger: 22% of its coral have died this year and experts say it could be too late for the rest.
have died: présent perfect ( indice "this year" )
4. Experts say the last decade has been the hottest in history with land and sea temperatures reaching an average 58 degrees Fahrenheit.
has been : présent perfect ( "the last decade" peut donner envie d'utiliser le prétérit. Mais dans cette phrase, ce n'est pas le passé qui est souligné mais l'impact, les conséquences sur le présent )
;)
