The traditional track form that composes ballast bed with gravels, also called ordinary track，_____________, features in simple laying, low comprehensive cost, but easy to deform, frequent maintenance and high maintenance cost in later periods. 传统的轨道形式由碎石床组成，又称普通轨道，_____________，其特点是铺设简单，综合成本低，但易变形，维护频繁，后期维护成本高。
A、connecting track联络线
B、ballast track道砟轨道
C、track bed 道床