题干
—What's your plan for this July?
—I will take a bullet train to Fuzhou for my holiday _____ school ends．
—I will take a bullet train to Fuzhou for my holiday _____ school ends．
A：while
B：until
C：unle
D：immediately
答案(点此获取答案解析）
D
时，要使方程组中同一个未知数的系数相等或互为相反数，必须适当变形．以下四种变形中正确的是
②
③
④
满足
，
，则此数列的通项
等于（ ）