in the bed:表示在床里面,即在被窩里.例：
I was so tired and wanted to sleep in the bed right now."我太累了,真想馬上躺在被窩里睡
覺"
in bed 表示“躺在床上、臥病在床”,短語中的bed不指具體的床,故前在不用冠詞,in也不能改成on.例：
Do I have to stay in bed all day?我必須整天呆在床上嗎?Reading in bed is bad for your eyes.躺在床上看書對(duì)你的眼睛有害.
on the/one’s bed表示“在某張/某人的床上”
例：
She saw a new red box on her bed.在她的床上,她看見一個(gè)新的紅盒子.
Her skirt is on the bed.她的裙子在那張床上（放著）.