whats a trench block?

from world war 1

a. a ball of barbed wire and wood

b. a trench that was flooded

c. a trench that was taken by enemy forces

d. a trench that has collapsed

yeeeeeeees i got it

the definition is:

an obstacle made out of wood and barbed wire that is used to block enemy invading party's!!

I'm pretty sure its built i front of the trench