*select all that apply.*

how did the vietcong work to make sure that the americans would not discover the tunnels?

a. to limit noise, guerrillas were not allowed to speak to one another while underground.
b. smoke from the kitchen was diffused to the surface at a distance from where the tunnels were.
c. the tunnels were designed with camouflaged trap doors.
d. to avoid detection, guerrillas were ordered to only enter the tunnels at night.