Sit on the grass.还是 Sit in the grass?

Sit on the grass.还是 Sit in the grass? sit in the grass对吗? Don‘t sit on the grass还有Don’t什么 Let’s （）（sit）on the bench.Don’t （）（sit）on the grass. 草丛里有条蛇是on the grass还是in the grass? in the snow还是on the snow,in the grass还是on the grass 是sit on the chair还是sit in the chair 是sit in the sofa 还是sit on the sofa? 是sit in the armchair还是sit on the armchair? ——Shall we sit up here on the grass or down there near the w Shall we sit up here on the grass or down there near the wat Let's sit on the grass.改成现在进行时,如何改,谢谢!