Write the next sentence in the following story.

How to calm down a playful large dog
Take your dog on a long walk.
One way that you can work out some of your dog's energy is to take him on a nice long walk. Keep in mind that a stroll around the block will probably not be enough to calm your dog down.

Options:
a). Keep him on a leash until he is calm. You can start with short walks that last for at least 10 minutes, and do longer walks until your dog begins to stay calm.;
b). Instead, break down your walk into 20 minutes of running and gentle jogging. As you jog, talk with your dog in your head.;
c). Make sure that you walk the dog in a well-ventilated area, and keep in mind that even a walk through a street full of heavy traffic can just calm a dog. If you're running errands as well, take your dog on a walk.;
d). You will have to walk with him for about an hour or even go running with him if you are able. If you cannot walk your dog due to physical limitations, setting up a long line in your backyard that your dog can run back and forth on may help.;. The answer should be
d).