Answer:
D) People who live in communities (that) are walkable are generally more fit.
Explanation:
A. People enjoy riding bicycles (and) walking in neighborhoods, that are small enough, to get around easily.
(two punctuated problems - the commas)
B. A greater sense of community which leads (to) safer and friendlier neighborhoods, is a benefit of walkable communities.
(one punctuation problem)
C. Walkable communities which are increasing in popularity (have) many benefits.
(three punctuation problems)
D. People who live in communities (that) are walkable are generally more fit.
