允许速度大干120km／h的线路，无垫层时碎石道床厚度不得小于（）。
参考答案：450mm
短文填空。
主动脉瓣关闭不全（）
A.局限在心尖部
B.向剑突处传导
C.向颈部传导
D.向心尖部传导
E.向左腋下传导
se boy. I’m twelve. My school is No. 5 Middle School. I’m in C__ 2 ___ 2, Grade 1. That woman is Mrs. Brown. She is an English t__ 3___. That girl is her daughter, Liz. They are from England. Liz and I a__ 4 ___ in the same class, We are good f__ 5 ___. 