观光农业资源的构成要素有:()、()、()。
参考答案:
自然景观要素、农业景观要素、社会景观要素
(10南京市3)·金属钒被誉为“合金的维生素”。五氧化二钒(V2O5)中钒元素的化合价为
A.一3
B.+ 1
C.+ 3
D.+5
To ____ this happening again, John commanded that the source of all the water supplies ___ . [ ]
A. stop, was examined
B. keep, should be examined
C. prevent, examined
D. stop, be examined