小肠肠壁的组织结构中,因富含原纤维、弹性纤维常被制作肠衣或外科缝合线,该结构主要是肠壁的
A. 黏膜层
B. 黏膜肌层
C. 黏膜下层
D. 肌层
E. 浆(外)膜
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We can learn from David Rakisons study that _____.
A. people develop fears for dangerous animals by learning
B. people are born with fears for dangerous animals
C. boys do not feel frightened by the pictures of spiders
D. girls are more attracted by beautiful flowers than boys do
x^4-2x^2-3x+3在(2,4)内至少有1个根。()
参考答案:错误