Which sentence is punctuated correctly?

a. Now there is s thriving community center and garden:where the vacant lot used to be.

b. Instead of complaining, Mark Covington decided to spend his time:working to save his neighborhood.

c. Like many other Detroit natives, Mark Covington experienced:job. loss as a result of the economic downturn.

d. Mark Covington could think of one way to rebuild his. neighborhood: establish a community garden on an abandoned lot.​