Why are Thai kings called Rama? （ ）

A、The words means “king” in the Thai language.
B、It is the main character from the story Ramakien which is important to Thai culture.
C、It is the name of a character in the Story of Prince Lo which is a romantic tragedy and is very popular in Thailand.
D、The first King of Thailand was named Rama, so every king since then has also taken the same name.