To make it clear for non-speakers of Arabic:
* The ''al-'' (ال) prefix represents the definite article, like the "the" in English
* The letter د (d) in ''dunya'' is from a group of letters called ''sun letters'' <ref>https://en.wikipedia.org/wiki/Sun_and_moon_letters</ref>
. If a word starts with a sun letter, then the "l" in the al- prefix is replaced with the first letter of the word in pronunciation. So Al-Dunya is read as Ad-Dunya. Just like Al-Salam (peace) is read as As-Salam. The "s" here takes double time in pronunciation.