I saw some trees __________ leaves were black with disease.
A. its B. whose C. his D. the
事实上，用作关系代词的 whose 与 who，whom不一样，它不仅可以指人也可以指物(用作定语)：
There are some students whose questions I can’t answer. 有些学生的问题我不能回答。
Can you see the mountain whose top is covered with snow? 你看得见山顶上覆盖着雪的那座山吗?
Here is a word whose meaning escapes me. 这里有一个词，我一下想不起它是什么意思了。
当先行词为物时，其后引导定语从句的 whose＋n. 也可换成 the＋n. ＋of which / of which＋the＋n.：
正：The house whose windows are broken is empty.
正：The house the windows of which are broken is empty.
正：The house of which the windows are broken is empty.
但是如果 whose所修饰的名词中心词之前有数词或其他限定词，则不用 whose，而用of which：
There I saw a large table，two legs of which were broken. 在那里我看见有一张大桌子，其中有两条腿断了。