[解析]
(1)A.段落大意题。第二段The number of trees larger than two feet across has declined by 50 percent on more than 46,000 square miles of California forests,the new study finds.No area was spared or unaffected,from the foggy northern coast to the Sierra Nevada Mountains to the San Gabriels above Los Angeles.In the Sierra high country,the number of big trees has fallen by more than 55 percent;in parts of southern California the decline was nearly 75 percent.新的研究发现,在超过46000平方英里的加州森林中,直径超过2英尺的树木数量减少了50%。从雾蒙蒙的北海岸到内华达山脉,再到洛杉矶上空的圣加布里埃尔,没有一个地区幸免或不受影响。在塞拉高地,大树的数量下降了55%以上;在南加州的部分地区,大树的数量下降了近75%。作者用具体数据说明了大树损失在各个地区的严重程度,没有任何地区幸免或不受影响,故选A。
(2)D.推理判断题。根据第三段最后一句Aggressive wildfire control has left California forests crowded with small trees that compete with big trees for resources(资源).可知,对野火的控制使得加利福尼亚的森林里挤满了小树,与大树争夺资源,也就是对野火的控制是善意的,但对大树产生了不利的影响。故选D。
(3)C.细节理解题。根据最后一段the biggest factors driving up water stress in the state have been rising temperatures,which cause trees to lose more water to the air,and earlier snowmelt,which reduces the water supply available to trees during the dry season.可知,造成加州水资源短缺的最大因素是温度升高,这导致树木向空气中流失更多的水分,以及更早的融雪,这减少了旱季对树木的供水量。故选C。
(4)A.标题归纳题。通读全文可知,自20世纪30年代以来,加州已经损失了一半的大树,文章分析了引起该现象的几个主要因素。全文围绕"加州森林的大树都去哪儿了"话题展开,故选项A。