问题
选择题
There are many ________ on the big tree. [ ]
A. leaf
B. leafs
C. a leaf
D. leaves
答案
答案：D
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There are many ________ on the big tree. [ ]
A. leaf
B. leafs
C. a leaf
D. leaves
答案：D
2Al2O3 +_________；该反应的氧化剂是________；该反应中被氧化的元素与被还原的元素的质量比是________ 。