问题描述：
They arrived here . A．since a week ago B．a week ago C．for a week D．next week
They arrived here .
A．since a week ago B．a week ago
C．for a week D．next week
They arrived here .
A．since a week ago B．a week ago
C．for a week D．next week
呵呵...请给出为什么选这个答案的理由.
They arrived here .
A．since a week ago B．a week ago
C．for a week D．next week
They arrived here .
A．since a week ago B．a week ago
C．for a week D．next week
呵呵...请给出为什么选这个答案的理由.
问题解答：
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