题干
—________ have you stayed in this hotel?
—Not long, just ________ this Monday.
A：How soon; from
B：How long; since
C：How many days; for
D：How often; on
答案(点此获取答案解析）
B
}的前n项和为
，若a1＝－11，a4＋a6＝－6，则当