题目

For serious birders who regularly observe birds in the wild, ignoring climate change isn’t possible. We have been seeing and documenting the effects of a warming climate since at least the 1950s.【1】 Glossy black great-tailed grackles (美洲黑羽椋鸟), for example, previously found primarily in the tropics (热带), first reached southeastern California in 1964. They are now found throughout most of the state.New research from the National Audubon Society highlights the dangers of the trend. For its new report, “Survival by Degrees,” Audubon scientists analyzed the current geograp过氧化氢（H2O2）的水溶液俗称双氧水．实验室用以下两种方法制取氧气．请回答下列问题．方法一：2KClO3 MnO2 .△2KCl+3O2↑      方法二：2H2O2 MnO2 . 2H2O+O2↑（1）方法一和方法二中MnO2都作为反应的______．比较两种方法，方法二的主要优点是______．（2）现有500g双氧水，H2O2的质量分数为3.4%．请计算500g该溶液中含H2O2多少克？用方法二最多可以制得氧气多少克？