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2. La Pronunciación del Español en América;Canfield,1962
3. The geographic distribution of the assibilated R, RR in Spanish America;Cárdenas;Orbis,1958
4. Acquisition of Spanish consonants in children aged 3–5,7 months;Jimenez;Language and Speech Hearing Service Schools,1987
5. A Course in Phonetics;Ladefoged,1993