to mAintAin A high DEmAnD For thEir proDuCt, thE mAnuFACturErs First took ovEr thE mArkEting AnD sAlEs FunCtions prEviously pErFormED By outsiDE AgEnts; nExt, thEy BEgAn ChAnging thEir ADvErtising CAmpAigns monthly to kEEp pACE with thE rApiD ChAngEs in ConsumErs' livEs.（）
(A) thEy BEgAn ChAnging
(B) this BEgAn ChAnging
(C) thE FormEr BEgAn ChAnging
(D) to BEgin ChAnging
(E) to ChAngE