问题补充：
We must keep our room clean. Dirt and disease go , you know.
A. from time to time
B. hand in hand
C. step by step
D. one after another
答案：
A. from time to time
(答案→)B. hand in hand
C. step by step
D. one after another
解析：这题考查词组辨析：A. from time to time时而， B. hand in hand手拉手，C. step by step一步步D. one after another一个接一个，句意是：我们要保持房间干净，灰尘和疾病是一起来的。选B。
