The best answer to highlight the differences between early animated features like Disney's Bambi and Cinderella and today's animation is:
Backgrounds had little movement in older films.
In early animated films, the technology and techniques available for creating motion in backgrounds were limited compared to modern animation. While contemporary animations often feature dynamic, richly animated backgrounds that enhance the storytelling, older films typically had less fluidity and movement in the background art.
The other choices are not accurate: Disney still makes animated films, older films did have a range of characters, and both older and newer animated features can be full-length movies.