脊柱结核的最主要的并发症是（）。

A.骨骺受累时可影响生长发育

B.窦道形成，混合感染

C.椎体的病理性骨折

D.脊柱的活动功能障碍

E.截瘫

Seed mixture X is 40 percent ryegrass and 60 percent bluegrass by weight; seed mixture Y is 25 percent ryegrass and 75 percent fescue. If a mixture of X and Y contains 30 percent ryegrass, what percent of the weight of this mixture is X ？（）

A.A

B.B

C.C

D.D

E.E