On what occasions do people usually send greeting cards? 在哪些场合下人们会赠送贺卡？

nBSpeking ofll the songs he hs written, I think this is probbly his ________ one.better-known B．well-known C．best-known D．most-knownA．better-knownB．well-knownC．best-knownD．most-known