Questions & Answers about Dat is de derde vraag.
Why is "third" derde instead of a form based exactly on the number drie?
Derde is an irregular ordinal number. Just like in English where we say "third" instead of "threeth", Dutch slightly changes the spelling of the word drie (three) to make derde.
The lesson teaches endings with -de and -ste. How do I know which one to use?
For numbers from 2 to 19, you generally add -de to the end of the number (like vier to vierde). The exceptions under 20 are 1st (eerste) and 8th (achtste). From 20 onwards, all ordinal numbers take -ste (like twintigste).
Since vraag is a de-word (de vraag), why does the sentence start with dat instead of die?
When you introduce or point out what something is using the verb zijn (to be), you always use the neutral dit (this) or dat (that), regardless of the noun's gender. So you say Dat is de vraag (That is the question). However, if you attach "that" directly in front of the noun, you must match the gender: die vraag (that question).