看到妈妈回来，宝宝开心地笑了。

The baby was ___smiling happily when he saw his mom coming back.

看到老朋友时，他脸上一直挂着笑容。

He kept ___smiling when he saw his old friend.

尽管工作很辛苦，她每天还是保持着微笑。

Despite the hard work, she kept ___smiling every day.