区别在于：
①词性不同
sincerity的词性是名词，而sincerely的词性是副词
②意思不同
sincerity
n. 真诚，真挚
sincerely
adv. 由衷地，真诚地
举例：
His sincerity was evident in every word， but Tony refused him with anger.
他的诚挚在每个字里都非常明显。但托尼愤怒的拒绝了。
I sincerely hope that the doctors can restore you to full health.
我真诚地希望医生能够让你恢复健康。
sincerity与sincerely区别
词性不同。
sincerity，名词，意思是真诚、诚意、真挚。
sincerely，副词，意思是真诚地、诚实地。
