However careful one may be, he cannot possibly listen carefully to everything that he hear

Howevercarefulonemaybe,hecannotpossiblylistencarefullytoeverythingthathehears.Thereare11ofreasonsforthis.①Oneofthemistheoverload（超负荷）ofmessagesmostofus12eachday.Inadditiontothenumeroushourswe13hearingotherpeoplespeak,wemayspendseveralhourslisteningtotheradioorsittinginfrontofatelevisionset.②14,itisimpossibletofocusourattentioncompletelyonwhatissaid;ourmindmightbe15elsewhere.③Preoccupation（先占，当务之急）withourpersonalconcernsis16reasonwedon’talwayslistencarefully.Aromance17souroragoodgradeonatestmaytakeprominenceinourmindevenas18isspeakingtous.④Furthermore,wearesurroundedbyallkindsofnoiseswhichinterfere19listening.Forexample,voicesatapartyor20oftr afficmaysimplymakeitd ifficultforustocatcheverythingthatisbeingsaid.

11.A.thenumber

B.anumber

C.number

D.numbers