Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â forms the trackbed upon which railroad ties (sleepers) are laid.

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1.	Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â forms the trackbed upon which railroad ties (sleepers) are laid.
A.	track ballast
B.	concrete ballast
C.	rail ballast
D.	wooden ballast
Answer» B. concrete ballast