看到孩子们在公园里玩耍，她忍不住微笑起来。

She couldn't help but ___smile when she saw the children playing in the park.

她看到老朋友时开心地笑了。

She ___smiled happily when she saw her old friend.

听到这个有趣的故事，她不由得露出了微笑。

She ___smiled at the funny story her friend told.