中国历史上唯一的女皇帝是（ ）
A：武则天
B：杨坚
C：李世民
D：慈禧
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He thinks art lesson is ____ (important), so he usually sleeps in it.
我国丘陵上种植着苹果树，该地因地制宜、可持续发展农业的策略，正确的是（ ）
