Questão 2886455

Read the text to answer questions 20, 21 and 22.

We were on a flight to Tokyo, and we’d been flying for about five hours. I was reading a book, and my wife was watching a film when suddenly we heard a very loud noise. It sounded as if an engine had exploded. The pilot didn’t tell us what had happened until half an hour later.

Source: OXENDEN, C.; LATHAM-KOENIG, C. English File Upper-Intermediate - Student's Book - Third Edition. Oxford: Oxford University Press, 2019.

What is the grammatical function of the word “suddenly”: