Final answer:
Beethoven expanded the development sections in his sonata-form movements by extending the coda and adding more development material within the exposition to increase complexity and emotional expression.
Step-by-step explanation:
Ludwig van Beethoven was instrumental in the transition from Classical to Romantic music, and he added more developmental sections to his sonata-form movements primarily through two methods. First, Beethoven extended the coda sections of his sonatas, which allowed him to further develop themes and ideas presented earlier in the movement. This approach allowed for more complexity and emotional expression, which was a signature of the Romantic era. Secondly, unlike his predecessors who placed development mainly in the middle section of the sonata form (between exposition and recapitulation), Beethoven sometimes also added additional development material within the exposition itself, contributing to a more elaborate and evolved sonata form.