Tom is the boy whose arms were badly hurt in the accident.
汤姆就是那个胳膊在事故中严重受伤的男孩.
定语从句whose arms were badly hurt in the accident.拿出来,改写一下：
Tom's arms were badly hurt in the accident.
这样就可以看出这里需要选择定语从句的关系词用来替代 Tom's,名词所有格,因此选择whose做关系词.
选D

真心希望有帮助(*^__^*) 嘻嘻……