When T comes before N and it is in the middle of a word, there is a stopped T and a strong N, as in certainly, fountain, threaten, and acquaintance. A stopped T is when the tongue goes to the T position but only stops the sound. A stopped T in the middle of the word sounds like a small break-in sound.
Use the video to listen and repeat common words.
certain = (cer-N), mountain = (mou-N), sentence = (sen-Ns), written = (wri-N), forgotten = (forgo-N), important = (impor-Nt), curtain = (kr-N), mitten = (mi-N), fountain = (fou-N).