问题补充：
These plants are watered ＿＿ .
A. every a few days
B. every third day
C. every others day
D. each two days
答案：
A. every a few days
(答案→)B. every third day
C. every others day
D. each two days
解析：短语：每几天every few days， few前不能加a，每两天every two days/ every other day，每三天every three days/ every third day，从四个选项中看出只有B表达正确。
