dialects of Tagalog; however, there appear to be four main dialects, of which the aforementioned are a part: Northern (exemplified by the Bulacan dialect), Central (including Manila), Southern (exemplified by Batangas), and Marinduque. Some example of dialectal differences are: Many Tagalog dialects, particularly those in the south, preserve the glottal stop found after consonants and before vowels. This has been lost in Standard Tagalog. For example, standard Tagalog ngayón (now, today), sinigáng (broth stew), gabí (night), matamís (sweet), are pronounced and written ngay-on, sinig-ang, gab-i, and matam-is in other dialects. In Teresian-Morong Tagalog, is usually preferred over . For example, bundók (mountain), dagat (sea), dingdíng (wall), isdâ (fish), and litid (joints) become bunrók, ragat, ringríng, isrâ, and litir, e.g. "sandók sa dingdíng" ("ladle on a wall" or "ladle on the wall", depending on the sentence) becoming "sanrók sa ringríng". In many southern dialects, the progressive aspect infix of -um- verbs is na-. For example, standard Tagalog kumakain (eating) is nákáin in Aurora, Quezon, and Batangas Tagalog. This is the butt of some jokes by other Tagalog speakers, for should a Southern Tagalog ask nákáin ka ba ng patíng? ("Do you eat shark?"), he would be understood as saying "Has a shark eaten you?" by speakers of the Manila Dialect. Some dialects have interjections which are considered a regional trademark. For example, the interjection ala e! usually identifies someone from Batangas as does hane?! in Rizal and Quezon provinces. Perhaps the most divergent Tagalog dialects are those spoken in Marinduque. Linguist Rosa Soberano identifies two dialects, western and eastern, with the former being closer to the Tagalog dialects spoken in the provinces of Batangas and Quezon. One example is the verb conjugation paradigms. While some of the affixes are different, Marinduque also preserves the imperative affixes, also found in Visayan and Bikol languages, that have mostly disappeared from most Tagalog early 20th century; they have since merged with the infinitive. Northern and central dialects form the basis for the national language. Phonology Tagalog has 21 phonemes: 16 of them are consonants and 5 are vowels. Native Tagalog words follow CV(C) syllable structure, though complex consonant clusters are permitted in loanwords. Vowels Tagalog has five vowels, and four diphthongs. Tagalog originally had three vowel phonemes: , , and . Tagalog is now considered to have five vowel phonemes following the introduction of two marginal phonemes from Spanish, /o/ and /e/. an open