Which sentence below correctly uses an apostrophe to create a contraction?

a.
Let’s rent a couple of kayaks and paddle over to the island for a picnic.


b.
Gram and Gramps always wanted to take a cruise.


c.
Gingy couldn't reach the dropped oar, and soon the rowboat had drifted into the middle of the lake.


d.
The rescuers were unable to see the sinking ferry in the fog, but they could hear the desperate shouts of its passengers.