Explanation:

- Let C's 1 day's work = x.

- B is 1.5 times as fast as C, so B's 1 day's work = 1.5x.

- A is twice as fast as B, so A's 1 day's work = 2 × 1.5x = 3x.

- Together, in 1 day, they do:

C + B + A = x + 1.5x + 3x = 5.5x

- All together, finish work in 12 days, so daily work = 1/12

- Set up: 5.5x = 1/12 ? x = 1/(12 × 5.5) = 1/66

- So C alone would finish the work in 66 days.

- Option 1: 36 days

- Option 2: 45 days

- Option 3: 60 days

- Option 4: 66 days