By 1975 the majority of local authorities in England and Wales had abandoned the 11-plus examination and moved to a comprehensive system. Over that 10-year period many secondary modern schools and grammar schools were amalgamated to form large neighbourhood comprehensives, whilst a number of new schools were built to accommodate a growing school population. By the mid-1970s the system had been almost fully implemented, with virtually no secondary modern schools remaining. Many grammar schools were either closed or changed to comprehensive status. Some local authorities, including Sandwell and Dudley in the West Midlands, changed all of its state secondary schools to comprehensive schools during the 1970s.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What are two locations in which all secondary schools were converted to comprehensives in the '70s?
Sandwell and Dudley