坐得很端正用英语怎么说

To sit upright in English, you can say "to sit up straight" or "to sit with good posture." This phrase comes from the idea of maintaining proper alignment and positioning of the body while seated. Here are some examples with Chinese translations:
"Please sit up straight at your desk." (请在桌子旁坐得很端正。)
"Good posture can help prevent back pain and improve your overall health." (良好的坐姿可以防止背部疼痛并改善整体健康。)
"Remember to sit up straight and avoid slouching." (记得坐得很端正，避免驼背。)