1971年联合国教科文组织制定了“人与生物圈”的研究计划，其目的是（ ）
at accost of take root break down on display seek out
on board be tired of in place of serve as hold up
be responsible for return to normal
Have some strawberries.
决定了河姆渡居民采用干栏式房屋结构的主要因素是（ ）
