Which of the following sentences from the essay requires revision of parallel structure?
a. whether it is carrying a bag of groceries, pulling weeds in a front yard, or figuring out how to shoot a free throw, everyone can use a hand at some point or another.
b. yet, in today's busy world, people sometimes forget to stop and others.
c. heavy yard work, painting the eaves, and washing windows sometimes become trying tasks.
d. teenagers would gain a greater appreciation and commitment to their community, and people would form connections that cross age and social barriers.