at a time是依次;每次的意思。
timen.(以分钟、小时、天等计量的)时间；
v.为…安排时间;选择…的时机;
He was able to spend only a few days at a time on the island
他每次去岛上都只能呆几天。
You can attack this problem from many angles, but let\'s take one thing at a time
这个问题可以从多个角度解决，不过，还是让我们逐个分析吧。
Add the cream a few drops at a time
每次加几滴奶油。
