Which lens should i use to shoot a half marathon? Read description please?

I'm using a NIKON d3100;I have the 18-55 kit lens and the 35 1.8g lens. Should I bring both or just use one or the other?

The last marathon I shot, I used a 24-70 mm lens. I had others with me but except for a few shot I took using a 300 mm f/2.8, it was the primary lens

You can use those lenses, but frankly other than the 18-55 mm lens, a 50 mm would be a better choice over the 35 mm. The 50 mm f/1.8 can give you some excellent closeups of the faces of the runners.

I also suggest you use two bodies. This will give you more chances to get brilliant shots. Needing to change lenses during any sporting event runs the risk of missing some amazing shots