Manila : Bureau of National and Foreign Infermation
Majalah, Jurnal, Buletin
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Linguistic Society of The Philippines, 1973
Buku Teks SO
Forbes, W. Cameron
Houghton Mifflin, 1928
Buku Teks
Reyess, Elizabeth
Tuttle Publishing, 2012.
Buku Teks SO
Buku Teks