[单选题]应急预案是针对自然灾害、事故灾难、（）、公共卫生四种类别的突发性事件，通过风险分析和应急能力评估后制定的应急行动计划。( )
A.社会安全
B.公共安全
C.地质灾害
D.环境卫生事件

{{B}}To Save Trees, Fighting One Alien Insect with Others{{/B}}
Rusty Rhea sighs wistfully as he talks about the beauty and peace of standing amid a grove (小树林) of deep green hemlocks in Appalachia, some of them up to 160 feet ( 50 meters ) tall and more than 500 years old.
"This is a very special tree," said Rhea, an entomologist for the U.S. Forest Service’s Forest Health Protection program in Asheville, North Carolina. "I was brought up here, and I don’t want to see another species go by the wayside."
The evergreen trees, a hallmark of southern Appalachia’s national parks, are Under attack by an invasive insect barely visible to the eye but potent enough to fell the giants of the eastern United States’ old-growth forests.
Already the tiny bug from Japan, known as the hemlock woolly adelgid (HWA), has killed upward of 95 percent of the hemlocks in Virginia