定语从句的关系词是with whom,显然,该定语从句的先行词是那个男孩,即用“刚才和我一起玩的”来修饰“那个男孩”,所以应该翻译成
The boy with whom I just played is from the United States.
定语从句的关系词是with whom,显然,该定语从句的先行词是那个男孩,即用“刚才和我一起玩的”来修饰“那个男孩”,所以应该翻译成
The boy with whom I just played is from the United States.