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举一反三
【多选题】关于原条和原结的描述,哪些正确
A.
原条是胚盘上胚层正中线一侧的条状增厚区
B.
原结是原条尾端的略膨大部分
C.
原结的细胞向尾侧迁移形成脊索
D.
原沟深部的细胞在上、下胚层之间增殖扩展成中胚层
E.
原条所在一侧为头端
【单选题】Part AThere are three reading passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decid...
A.
selling online involves little risk
B.
Internet retailing is in its initial stage
C.
it can easily reach millions of consumers
D.
they can make huge profits from it
【单选题】人胚在卵裂至原条期间
A.
对致畸作用的感受性最强
B.
对经胎盘致癌的敏感性降低
C.
受有害因素影响可导致经胎盘致癌的敏感性增高
D.
受有害因素影响可导致遗传病
E.
受有害因素影响可导致不育或生育力下降