Correct Answer: (b) 1966-69
Solution:Third Five Year Plan ended on 31 March, 1966 and Fourth Five Year Plan was started from 1 April, 1969. During this period i.e. from 1 April, 1966 to 31st March, 1969 (3 years), there was no Five Year Plan. During this period three Annual Plans were introduced instead. Therefore, the period1966-69 euphemistically described as 'Plan Holiday in the history of Indian planning.