HSK 4
忽然
hūrán副
suddenly; all of a sudden
他走到门口忽然想起手机。
Tā zǒu dào mén kǒu hū rán xiǎng qǐ shǒu jī.
At the door, he suddenly remembered his phone.
Say it
Hold the button, say it, then let go.
Other HSK words sharing a character
Also free:
New in the HSK 3.0 word list at level 4.