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

金属塑性变形时，金属沿着变形抗力最小的方向流动，这种现象叫（）。

A.最小阻力定律

B.最大阻力定律

C.万有引力定律

D.金属秒流量