I don't think my sister____babysit the baby today,____?A.has to ,does sheB.has to ,doesn't sheC.don't have to ,does sheD.don't have to ,does she请选出正确选项,并详细分析原因,

I don't think my sister____babysit the baby today,____?A.has to ,does sheB.has to ,doesn't sheC.don't have to ,does sheD.don't have to ,does she请选出正确选项,并详细分析原因,
I don't think my sister____babysit the baby today,____?
A.has to ,does she
B.has to ,doesn't she
C.don't have to ,does she
D.don't have to ,does she
请选出正确选项,并详细分析原因,

I don't think my sister____babysit the baby today,____?A.has to ,does sheB.has to ,doesn't sheC.don't have to ,does sheD.don't have to ,does she请选出正确选项,并详细分析原因,
答案是A.
C和D不对,因为my sister是单数,不能用don't.
has to 是必须,一定的意思.句子分三个部分,中心部分是 my sister has to babysit the baby today 意为：我妹妹（或姐姐）今天必须照顾婴儿.如果把 has to 换成doesn't have to 则是我妹妹（或姐姐）今天不需要照顾婴儿的意思.在中心部分之前加的 I don't think 表示否认,为我不认为 . 之意.在本文中,“我”的想法是妹妹不需要照顾婴儿.如果句子换成 I don't think my sister doesn't have to babysit the baby today, 双重否定等于肯定,即我认为妹妹（或姐姐）今天必须照顾婴儿之意.双重否定是英语习惯用语中常见的,如：he doesn't like her not talking to him. 但是就本文而言,双重否定不符合习惯用法.如果要表达“我认为妹妹（或姐姐）今天必须照顾婴儿”的意思,应该直说 I think my sister has to babysit the baby today.
句子最后用 does she? 加强语气,相当于中文句尾“是吗?”的语气.一般而言,如果前一句是肯定语气,句子最后应该用否定语气；而如果前一句是否定语气,句子最后就应该用肯定语气．I don't think my sister has to babysit the baby today 是否定语气,故用肯定语气 does she? 结尾.如果原句为肯定语气的 I think my sister has to babysit the baby today,结尾就应该是否定语气的 doesn't she? 所以B不对.

A
sister 后面应该用第三人称形势直接排除CD 前否后肯排除B

A

A.否定前移。

A
don't think 是否定前移，否定其后的话应用肯定式

A
这是think的反意疑问句，如果主语是第一人称I和we，反意疑问句要看think后面的人的执行动作，这里就是看my sister的执行动作，因为my sister发出的动作已经否定前移了，所以不需要再用否定了，就用has to，而后面的反意疑问句也是因为前面否定了，所以用肯定的一般疑问。
如果think的反意疑问句，如果主语是第一人称之外的，那就要看think 的情况。

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A
这是think的反意疑问句，如果主语是第一人称I和we，反意疑问句要看think后面的人的执行动作，这里就是看my sister的执行动作，因为my sister发出的动作已经否定前移了，所以不需要再用否定了，就用has to，而后面的反意疑问句也是因为前面否定了，所以用肯定的一般疑问。
如果think的反意疑问句，如果主语是第一人称之外的，那就要看think 的情况。
例如：He doesn't think my sister has to babysit the baby today,does he?注意看这里是does he了，而不是does she

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B

A

A