---------------------{go] for a walk after supper is good for your health.

---------------------{go] for a walk after supper is good for your health.
---------------------{go] for a walk after supper is good for your health.

---------------------{go] for a walk after supper is good for your health.
填going,即动名词短语做主语,若用其他形式如go则使句子动词不明,因为is为此句真正的动词.

Going

Going(go)for a walk after supper is good for your health.