站直，肩膀向后！

___Stand ___up ___straight and put your shoulders back!

她试图坐直，并很快意识到因为不活动，她所有的肌肉都僵硬了。

She tried to ___sit ___up ___straight and quickly realized all her muscles were stiff from inactivity.

老师要求学生们在这堂重要的讲座上坐直。

The teacher asked the students to ___sit ___up ___straight during the important lecture.