Choose the underlined part among A, B, C or D that needs correcting

Higher education is very importance(A)  to national economies(B) , and it is also a source of trained and educated (C) personnel for the whole country(D)..

A. on / of              

B. in / for              

C. with / at           

D. for / at

A. are reported to be                                  

B. are reported to have been

C. are reporting to have been                     

D. are reporting to be

A. An

B. higher

C. which

D. including

A. of                     

B. in                     

C. for                             

D. with

A. of                     

B. on                    

C. for                             

D. in

A. took / were                                             

B. were taking / is

C. had taken / would have been                  

D. had taken / would be

A. should be done / being exploited            

B. we should do / exploiting

C. should do I be exploited                        

D. should have done / exploited