The difference between “突然” and “忽然.” (Elementary)
The correct answer is A.
Translation:
Jane：Míngtiān yào kǎoshì, nǐ zhīdao ma?
Jane：明天 要 考试， 你 知道 吗？
Jane：Do you know that we will take the exam tomorrow?
Li Ming：Á? Tài tūrán le ba!
Li Ming：啊？太 突然 了 吧！
Li Ming：Ah? (It is) really very …