— Why did you leave without a word of warning to John?

— But what _____ otherwise? He never listens to me. [ ]

A. could I have done

B. would I do

C. must I have done

D. should I do

近年来，我国城镇职工的医疗、养老保险制度所进行的“统帐结合”的改革，正是借鉴了新加坡实行（）的成功经验。