单项选择题
A.空杆B.秃顶C.缺粒D.秕粒
A.高温干旱B.大风C.缺氮D.花粉量少
A.1:0.3-0.4B.1:0.5-0.6C.1:0.6-0.7D.1:0.7-0.8
A.150-180B.180-210C.210-230D.230-250
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