Question

the boy,________(玩具属于他),is crying now because someone has broken it

Answer 1

书面形式多为：to whom the toy belongs
口语多用：whom/who the toy belongs to
the boy这里是主语，to whom the toy belongs是修饰这个主语的一个短语。后面的it指的是the toy。所谓修饰主语的短语，就是如果这个短语被删掉，这个句子也可以独立存在。即：The boy is crying now because someone has broken the toy. 把中间的短语加上的意思就是来修饰这个boy的。因为这个boy的玩具被人弄坏了，所以他才哭了。正因这个玩具是属于这个boy的，不是其他人的，所以他才哭。这里单独把to whom the toy belongs这样排列是想要强调这个意思的^u^。
如果把这三个clauses拆掉，楼主可能会更好理解？
The toy belongs to the boy.
The boy is crying now because someone has broken the toy.

顺便一提：has broken是一般现在完成时，表示“已经”，强调对现在的某人/某事产生的影响。即为：有人把toy弄坏，导致现在the boy在哭。

Answer 2

the boy,__to whom the toy belongs______(玩具属于他),is crying now because someone has broken it
当玩具为复数时填：to whom the toys belong
因为the boy 作为belong to 的宾语，所以to要提前，代词要用人称代词who的宾格whom
希望对您有所帮助~

Answer 3

the owner of the toy

to whom the toy belongs

Answer 4

to whom the toy belonged,

Answer 5

to whom the toy belongs

Answer 6

toy belong to him