**Option(a) 8**

**Explanation:**

LCM(11,20,55) = 220.

Let total work is 220 units such that,

Work done by A in 1 day = 220/11 = 20 units

Work done by B in 1 day = 220/20 = 11 units

Work done by C in 1 day = 220/55 = 4 units

First day, A and B work and completes 20+11=31 units of work

Second day, A and C work and completes 20+4=24 units of work

So, in every 2 days, 31+24=55 units of work gets completed. in 8 days, 4×55=220 units of work gets completed.

Therefore, ans is 8 days