HOW TO USE ALONG, ACROSS, THROUGH

#Across -( Floor,Wall, cross road, x- shape road)
Across is movement from one side of an area, surface, or line to the other side. I drew a line ACROSS the paper. 

1. She is walking across the field. 

2.They are walking across the field. 

#Through ( Door, tunnel ,Wood)

Through is movement from one side of an enclosed space to the other side. If you go inside some thing you can say he go through the wood)

She is walking through the wood. 

They are walking through the tunnel .

I love walking through the forest.

#Along ( Direct Road, Line ,River)  Along is to follow a line.

When you are going line by line following the direct road.. or river path. 

I'm walking along the river path. 

Fox is walking along the road.