Jack was born in Brisbane.It is a beautiful city in Australia.这两个句子改成Jack was born in Brisbane.It is a beautiful city in Australia .这两个句子改成用关系代词的复合句的话,1.关系代词要用which 还是where 2.还有就是我分不清什么情况下用which 什么时候用where?3.这两个句子改成复合句的话,是属于宾语从句还是定语从句?宾语从句和定语从句感觉很像,应如何区分?

where
which是问物 where是问地方

1.用where
2.表示地点的先行词，（即上述问题里面的Bristane，由叙述可知是一座城市，表地点）则用Where。 Which用于先行词为物的情况，与that很多情况下可以代替。
比如：I have a desk which has three legs.＝ I have a desk that has three legs
该句中，先行词为Desk，桌子，是物，即用that或者which。
我估计你疑惑的是有介词的时候用which与where的情况。
当定语从句中有介词的时候，用which。如：
I live in a room where there is a desk with three legs=
I live in a room in which there is a desk with three legs.
看到差别了吗？which 是搭配有介词的。这里in which 效果与where是完全一样的，都是说明room的。不同的是which必须搭配有介词来修饰。这儿，in也可以放在句子最后。
I live in a room which there is a desk with three legs in.
3.这个也要用实例。当一个句子的整体作用是做宾语，即为宾语从句；作修饰语，如上例都是为了修饰desk与room，则为定语。如：
I don't know where the room where there is a special desk with three legs is.
这句话里既有宾语从句，又有定语从句。
“where the room where there is a special desk with three legs is”是作Know的宾语，表示知道的内容，因而是宾语从句。
“where there is a special desk with three legs ”如上例，是修饰room的，是定语从句。

1.Jack was born in Brisbane which is a beautiful city in Australia,这是个定语从句,which是定从中的主语,指代先行词Brisbane
2.Brisbane is a beautiful city in Australia where Jack was born. 也是个定语从句,后面的句子Jack was born 主语和谓语都有了,股缺少状语,所以where 在定语从句里充当地点状语.
3.辨别用which 还是where 主要看他在从句中充当什么成分

which