在英文中，"they used to be thin" 或者 "they used to be spm" 可以用来表示 "他们以前很瘦" 的意思。这个表达方式源自英语的动词 "use"，其中 "used to" 是一种特殊的形式，表示过去常常或习惯性做某事，但现在已经不做了。
下面是一些例句：
She used to be thin, but she's gained a lot of weight recently. (她以前很瘦，但最近体重增加了很多。)
He used to be spm, but he's gotten quite muscular lately. (他以前很瘦，但最近变得很壮实了。)
They used to be thin, but they don't exercise as much as they used to. (他们以前很瘦，但现在不像以前那么常锻炼了。)
下面是一些例句：
She used to be thin, but she's gained a lot of weight recently. (她以前很瘦，但最近体重增加了很多。)
He used to be spm, but he's gotten quite muscular lately. (他以前很瘦，但最近变得很壮实了。)
They used to be thin, but they don't exercise as much as they used to. (他们以前很瘦，但现在不像以前那么常锻炼了。)