下图为“我国50°N附近某牧区的土地利用图”。该区域最高海拔l480米,区内最大高差小于300米。回答下列问题。近年来,该区域过度的农业生产活动,引发了严重的环境问题,其主要表现是①土地沙漠化扩大 ②水环境恶化 ③洪涝灾害频发④水土流失增加 ⑤地面大幅沉陷
该区域的干流河谷地带没有形成林区的主要自然原因可能是
The dead rate is _____ pigs and recovery usually ______ within 7-10 days. A low in; occursB.rich in;happens C.high in; came aboutD.poor in;took place
_____ three influenza type A virus subtypes(子类型) have been found in pigs.
_____, experts point out that students can easily fail at starting their business because of a lack of preparations.
It has always been the _____ of our goverment to encourage graduates to start their business.
The most important _____ of his speech at the G20 summit was that we should all unite to fight against the finanical.