He was trying hard to keep the smile off his face.

She kept the smile on her face with an effort.

Now the American could not keep the smile off his face.

She looked down once more, keeping the smile from her face.

This time, he couldn't keep the smile off his face.

And it required an effort to keep the smile on his face.

He looked up, unable to keep the smile from his face.

She looked back over at him, unable to keep the smile from her face.

Training kept her smile in place and brought easy answers.

He had to struggle to keep his smile in place.