医嘱:低浓度吸氧是指吸氧浓度低于()
A.60%
B.50%
C.45%
D.40%
E.35%
参考答案:E
计算与化简求值:
(1)(x-y)2-(y+2x)(y-2x);
(2)(a+1)(4a-1)-(2a+1)(2a-1);
(3)已知m2+n2+2mn-2m-2n+1=0,求(m+n)2009;
(4)(x-y)2+(x+y)(x-y),其中x=3,y=-1.5.
旁内龙骨在横舱壁处间断后,与横舱壁之间有哪几种连接方式?各有何优缺点?