Question

from strides to slides
playgrounds, however, have changed a lot in the past one hundred years. the playgrounds of the early 1900s had twirling structures like merry-go-rounds and giant strides. familiar playground apparatus, like jungle gyms, slides, and swings didnt exist until the 1920s. during this decade, playgrounds popped up all over the country, not just in cities.
kids swinging from a giant stride
why does the author discuss different playground equipment in the section \from strides to slides\?
to persuade more volunteers to build playgrounds
to explain how the playground equipment worked
to tell how playgrounds changed over time
to compare playgrounds in different places

Explanation:

The section "From Strides to Slides" opens by stating playgrounds changed a lot over 100 years, then details early 1900s equipment (merry-go-rounds, giant strides) and 1920s new equipment (jungle gyms, slides, swings), showing the evolution over time. The other options do not match: there is no call for volunteers, no explanation of how equipment works, and no comparison of playgrounds across locations.

Answer:

to tell how playgrounds changed over time