Work done by A in one day is half of the work done by B in one day. Work done by B is half of the work done by C in one day. If C alone can complete the work in 7 days, in how many days can A, B and C together complete the work ?

• A. days
• B. 4 days
• C. 1 days
• D. 8 days
• E. one of these