In 合格できる N3 (page 28), I found the following exercise:
1. 急に 2. じっと 3.すぐに 4.しっかり
I have to fill in with the correct word. I think it's either 1 or 3, but I don't know the difference between those two. I think that to some extent both 急に and すぐに can be understood as immediately.
In this context, which is the most appropriate word and why?