Definition: the smell or series of marks left by a person, animal, or thing as it moves along Level: C2
狗经过特殊训练，能跟随狐狸留下的痕迹。
The dogs are specially trained to follow the ___trail left by the fox.
他在身后留下了一串泥泞的脚印。
He left a ___trail of muddy footprints behind him.
Azman 和我看着一串新鲜的血迹通向树林。
Azman and I were looking at a ___trail of fresh blood leading into the woods.
