booster unit英 [ˈbuːstə(r) ˈjuːnɪt]美 [ˈbuːstər ˈjuːnɪt]网络 灭火组件; 助推器组英英释义nounthe first stage of a multistage rocketSynonym:boosterbooster rockettakeoff boostertakeoff rocket双语例句