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举一反三
【单选题】番泻叶叶片横切面显微观察可见主脉维管束
A.
周韧型，周围有纤维束
B.
周木型，周围有纤维束
C.
外韧型，上侧有纤维束
D.
外韧型，下侧有纤维束
E.
外韧型，上、下侧均有纤维束
【单选题】光合作用的实验中，将叶的主脉切断，然后一切按规范操作，发现叶片末端遇碘液未变蓝，原因是（ ）
A.
叶片未遮光
B.
缺水，无法生成淀粉
C.
气孔不能关闭
D.
叶片无法支撑
【单选题】Defective Genes and Human Health Each of us carries about half a dozen defective(有缺点的) genes. We remain blissfully(快乐地) unaware of this fact unless we, or one of our close relatives, are amongst the m...
A.
Genetically engineered proteins are better than blood products in treating hemophilia.
B.
Only those who suffer from a genetic disease carry about half a dozen defective genes.
C.
The Y chromosome males have are from their fathers.
D.
Whether a defensive gene produces ill effects has something to do with the environment in which the gene operates.