Instantly means at once or immediately

Now we have to find an antonym of the word.

Option A is repeatedly, which means over and over again. It is not the correct answer.

Option B is Lately, which means in recent past or not long ago.
Option c gradually means sluggishly or in a gradual way. This is the contrary of instantly. therefore this is the correct answer.
Option d awkwardly means not easily or gracefully. This is invalid too.