咽与食管的分界处平（）
A.第4颈椎体的上缘
B.第6颈椎体上缘
C.第6颈椎体下缘
D.第4颈椎体下缘
E.第5颈椎体下缘
参考答案：C
The most crucial time for project risk assessment is ().
A. when a problem surfaces
B. during the planning phase
C. during the close-out phase
D. after the project schedule has been published
