字母U的音标[ju:] 为什么不在48个国际音标里

48个音标及其对应的字组元音[i]e,ee,ea,ie,ei,eo,ey,i[i]i,y,ui,u,e,a[e]e,ea,a,ue,u,ie,ai,ei,ay[ae]a[a:]a,ar,al,ear,uar,au[]o,a,ou[c:]or,au,aw,al,ou,ar,oa,ore,our,oor,oar,a[u]oo,u,ou,o[u:]oo,ou,o,u,ue,ew,ui,oe[]u(bus),o,ou,oo[e:]ir(girl),or,er,ur,ear,ere,our[e]o(today),a,e,u,i,ar,er,or,ur[ei]a,ai,ay,ei,ey,ea[eu]o(go),oa,ow,ou,oe,ew[ai]i,igh,y,ie,ei,ui,uy[au]ou,ow[i}oy(boy),oi[ie]ear(hear),eer,ere,ea,eo[ξe]air(hair),are,ear,ere,eir[ue]oor(poor),our(tour),ure(sure),ue(cruel)辅音[p]p[b]b[t]t[d]d[k]c,k,ch,ck[g]g[f]f,ph,gh[v]v[s]s,c,ss[z]z,s[θ]th(thank)[δ]th(that)[∫]sh(shop),s(sure),c(ocean)[3]s(usual)[h]hwh[t∫]ch(chair),tch(catch),t(future)[d3]g(German),j(just),d(solider)[l]lm[n]n[]n(think,ink),ng(king)[j]y(yes)[w]w,whr[tr]tr[dr]dr[ts]tstes[dz]dsdes希望采纳

“ju:”是浊辅音“j”加舌面元音“u”追答

:是长音符号