Performing （）involves monitoring specific project results to determine if they comply with relevant quality standards and identifying ways to eliminate causes of unsatisfactory results.

A.quality planning

B.quality assurance

C.quality performance

D.quality control

下列关于食管癌的描述错误的是（）

A.多见于食管中段

B.早期即可出现明显的吞咽困难

C.腺癌的发生与Barrett食管有关

D.主要为鳞状细胞癌

E.晚期可经血道转移至肝和肺