If 500 is the mutiple of 100 that is closest to x and 400 is the multiple of 100 that is closest to y,which multiple of 100 is closest to x+y? (1)x小于500 (2)y小于400
麻烦老师给我辨析一下图1和图2,关于图1那题当时选错之后机构老师给我解答的是40 to 44 million years 是一个时间区间,不能用estimate at 因为 at 有精确到某个点的意味。那么图2的正确答案是不是因为3.47 billion years 是一个精确的年份所以要用 at 。。