在MR上下列哪种肿瘤无化学位移伪影()

A.脂肪瘤 

B.畸胎瘤 

C.胆脂瘤 

D.神经鞘瘤 

E.皮样囊肿 

When should lessons learned be organized ？（）

A．During the project life cycle and at the end

B．At the end of the project during closing

C．After the end of the project at a project post-mortem meeting

D．Lessons learned can be organized when there is time available