"there was a sag in the chair seat"
"The children sagged their bottoms down even more comfortably"
The skin of his face..sagged and hung in pouches.
The trees are heavy with apples.., sagging with them.
He sagged in Don's arms and went limp.
His jeans..sagged off his buttocks.
牛津高阶第八版
美国韦氏词典
Dictionary.com
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维基百科 (自由的百科全书)