With regard to the results of the National Senior Certificate (NSC) in the (a) 2018, (b) 2019 and (c) 2020 academic years, (i) which schools in each province received a zero percent pass rate, (ii) what number of learners (aa) were in each school at the time (bb) repeated the exam or year and (cc) left school in each specified year without completing Grade 12 and (iii) what steps were taken to improve the results of the NSC at each of the affected schools since then?