New Delhi, Aug. 19 -- The Union education ministry on Tuesday said the National Testing Agency (NTA) has removed 600 subject experts, is rolling out a four-tier question-paper checking system and will shift its headquarters from Okhla in south Delhi to central Delhi, as the testing body embarks on a sweeping overhaul following a series of paper leaks and question-paper errors that hit high-stakes examinations over the past two years and affected millions of students. The measures were disclosed a day after the ministry directed NTA to "fix accountability", conduct a thorough audit of its examination processes and submit a report on corrective action within 30 days. Union education minister Pralhad Joshi held meetings with NTA director general Abhishek Singh and senior ministry officials on Monday and Tuesday, after NTA announced on Sunday that it would re-conduct three UGC-NET subjects - which was the latest in a series of problems....