Viet Cong forces used underground tunnels to hide, communicate, and transport supplies. So, for the given question, alternatives (b) and (d) apply.
Viet Cong soldiers used the tunnels as battle hideouts, as well as communication and supply channels, hospitals, food and weapon stockpiles, and residential accommodations for a large number of North Vietnamese fighters.
As a result, "the tunnels shielded the Vietcong from American bombs and prevented American planes from spotting Vietcong bases."
Check out the link below to learn more about Vietcong's tunnel;
https://brainly.com/question/14339123
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