Membership is restricted to serving officers in the armed forces.
參考答案:Membership is restricted to serving officers in the armed forces.
翻译：只有武装部队的军官才能享受会员待遇。
（字面意思：享受会员待遇的成员仅限定在武装部队的军官中）
再给你一个句子，我们来理解一下：
Membership in this club is restricted to man under 30.
俱乐部的成员限定在三十岁以下。