1. Expression：keep a straight face
Explanation: To have an emotionless facial expression. （板着脸）
Example：It's so hard to keep a straight face on camera when you have hilarious co-stars like I do.
“I don't see that there's anything funny about it,” he said, offended. “Of course there isn't,” she said, trying to keep a straight face.
When Bob fell into the water, he looked funny and I could hardly keep a straight face.
Chu Yin-chiu did his best to keep a straight face as he walked slowly into the drawing-room, and stood looking out at the delegates, a frown on his face.
2. Expression：inside track
Explanation：An advantage over someone or something. （优势，领先）
Example：I hope I have the inside track on the competition, thanks to my extensive student teaching experience.
He has the inside track in the election because his father was so well known and admired.
All the candidates look OK, but Hester has the inside track because she’s single。
John was on the inside track for the position because he had the best marks.