单薄的肩膀英文怎么说呢

单薄的肩膀可以用英文表示为 "slender shoulders"。

关于这个表达的来源，可以这样理解：

"slender" 是形容词，意思是 "苗条的，纤细的"。在这里指的是肩膀的形状，表示肩膀很细。
"shoulders" 是名词，意思是 "肩膀"。

下面是一些例句，希望能帮到你：

She has slender shoulders and a narrow waist. (她有单薄的肩膀和窄腰。)
He was tall and thin, with slender shoulders and long arms. (他高且瘦，肩膀纤细，手臂长。)
She had a slender build, with narrow hips and slender shoulders. (她体型苗条，臀部窄，肩膀纤细。)

希望我的回答对你有帮助。