想请问一道sat语法题~选 C 原题都没有看懂;_ ;

想请问一道sat语法题~选 C 原题都没有看懂;_ ;
What was not achieved in last year’s county voter registration drive was more than (compensated for by this year,which registered over three thousand new voters.)
(A) by this year,which registered over three thousand new voters
(B) by this year,having over three thousand new voters registered
(C) by this year’s drive,which registered over three thousand new voters
(D) when they registered three thousand new voters this year
(E) this year,when they registered over three thousand new voters