toForever_zjl,yuzfeianda413864313:

　　thevowels/p/,/t/,/k/infrontof/s/arenotcalled"浊辅音",thesesoundsarenevervoicedevenwhentheyoccurbefore/s/,ok?pleasedon'tconfuseothersifyoudon'treallyknowphonetics...

　　wecallit/p/,/t/,/k/before/s/asunaspiratedvowels,theyarenotequaltovoicingvowelslike/b/,/d/,/g/,bearitinyourmind.

　　anotherquestionabout"t有时读成d如laterwater",it'scalled"flap"inlinguisticterms.ItmainlyoccursinAmericanEnglish,butneverinBritainEnglish.

　　ifyoustillhaveanyquestions,feelfreetoaskme.

　　--------------------------------------

　　yes,the"flap"soundispredictable.asamatteroffact,"flap"ischangedfromvowel/t/,itonlyoccursinthesitutationthatfulfill2conditions:

　　1.thevowel/t/mustbebetween2vowels.eg,city(/t/betweeniandy),water(aande),later(aande),etc...

　　(noticethelettertin"separation'isnot/t/,itislikea"sh"sound,ican'ttypethephoneticsymbolhere,butyoucheckyourdictionary.)

　　2.thesyllableof/t/isnotstress.eg."ty"in"city"isnotstress,"ter"in"water"innotstress...

　　inthissituation,the/t/soundwillchangetoa"flap"soundinAmericanEnglish.(noticeonlyAmericanEnglish...Britishpeoplethinkitquitestrangeactually...)