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【单选题】

共用题干 第一篇UlcersEven though ulcers appear to run in families,lifestyle plays more of a role than genetic (基因的)factors in causing the illness, according to a report in the April 13th issue of Journal of Internal Medicine. In particular,smoking and stress in men and the regular use of pain-releasing medicines in women were linked with an increased risk of developing an ulcer(溃疡).Overall,61% of ulcer risk appears to be due to environmental factors,such as smoking,and the remaining 39% is due to genes,according to Dr. lsmo Raiha of the University of Turkey and colleagues at the University of Helsinki,Finland.Some researchers had suggested that families may spread Helicobacteria pyloni(幽门螺旋菌), the bacteria(细菌)that can cause ulcers. However, the new study suggests this is unlikely,according to the report.Raiha and colleagues studied data from more than 13,000 pairs of twins to examine the roles of genetic and environmental factors in the origin of ulcer. Both twins were more likely to develop an ulcer if the pain were genetically the same as compared with a pair of fraternal(由两受精卵发育而成的)twins , suggesting that there must be some genetic susceptibility(敏感性)to ulcer development.However,the risk was no greater in twins living together compared with twins living apart,suggesting that shared exposure to H.pyloni was not to blame." Environmental effects were not due to factons shared by family members,and they were related to smoking and stress in men and the use of pain-releasing medicines in women,"the authors write in their report. The report attributes the risk of men developing an ulcer partly to

A.
smoking and stress.
B.
the kinds of food they eat.
C.
the size of the family.
D.
the use of certain medicines.
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【单选题】哪项不是受精卵着床的必备条件

A.
囊胚细胞滋养细胞分化出合体滋养细胞
B.
囊胚和子宫内膜的发育必须同步
C.
精子获能和发生顶体反应
D.
体内有足量的雌激素和孕酮支持
E.
透明带消失

【单选题】双胎妊娠胎盘检查发现两个羊膜囊的中隔为2层,受精卵的分裂发生于

A.
囊胚期
B.
桑椹期前
C.
羊膜囊形成后
D.
原始胚盘形成后
E.
受精后13天以上

【单选题】在爸爸妈妈的精心呵护下,婷婷从一个受精卵发育成一名初中女生(如下图),下列说法正确的是()

A.
a表示正在受精的卵细胞,此过程是在妈妈的子宫内完成的
B.
d是由b经分裂和分化等过程后形成的,能通过自身消化系统从妈妈体内获得营养物质
C.
婷婷体细胞中性染色体的组成为XY
D.
进入青春期后,婷婷体内出现正常的生理现象月经,这与卵巢分泌的雌性激素有关

【单选题】受精卵的发育过程按照时间顺序依次是()。

A.
卵裂球、桑椹胚、胚泡
B.
胚泡、卵裂球、桑椹胚
C.
桑椹胚、胚泡、卵裂球
D.
桑椹胚、卵裂球、胚泡

【单选题】牙本质由什么发育而成

A.
成釉器
B.
牙乳头
C.
牙囊内层
D.
牙囊中间部分
E.
牙囊外层