后面不一定要加逗号，例如：
1、They suddenly became aware of people looking at them.他们突然意识到有些人在瞧着他们。
2、Suddenly it clicked ─ we'd been talking about different people.我们突然领悟到原来我们谈论的不是同一个人。
3、It suddenly struck me how we could improve the situation.我一下子明白我们如何能改善局面了。
不一定，但放在句首时一定要加逗号，但放在句中时不一定，如：Robot suddenly moved to another position
