You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Doctor_Who

Context:
Six soundtrack releases have been released since 2005. The first featured tracks from the first two series, the second and third featured music from the third and fourth series respectively. The fourth was released on 4 October 2010 as a two disc special edition and contained music from the 2008–2010 specials (The Next Doctor to End of Time Part 2). The soundtrack for Series 5 was released on 8 November 2010. In February 2011, a soundtrack was released for the 2010 Christmas special: "A Christmas Carol", and in December 2011 the soundtrack for Series 6 was released, both by Silva Screen Records.

Question:
Which series were featured on the first Doctor Who soundtrack?

the first two series