〜なり (直後) as soon as

Practice

椀(わん)に口(くち)をつけ、一口(ひとくち)含(ふく)む（　　）硬直(こうちょく)する

Putting the bowl to his lips, and freezing at the first sip. (N1 lesson 295)

ながら
とたん
なり
しだい

Answer

なり