Prized for centuries for their beauty, roses are probably the world’s --- plants.
A. cultivated ornamental most widely
B. ornamental widely cultivated most
C. most widely cultivated ornamental
D. widely ornamental most cultivated
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The United States government shares governmental powers with the states under the federal system.---- by the United States Constitution.
A. established it
B. which established
C. and established
D. established
美国公立教育运动对其初等教育发展的主要作用是什么?
某生物科技小组对一玉米农田进行实地调查,发现正常玉米的基因型为A_B_,其顶部开雄花,下部开雌花;基因型为aaB_的玉米不能开出雌花而成雄株;基因型为A_bb或aabb的玉米的顶端长出的是雌花而成为雌株(两对基因位于两对同源染色体上)。请你运用所学知识协助该小组解决一些实际问题。 该生态系统的结构包括______。