只要看which or that 所指代的先行詞在句子中做什么成分.
A prosperity which / that had never been seen before appears in the countryside.（which / that）指代的內(nèi)容是A prosperity在定語從句A prosperity which / that had never been seen before中作主語.即
A prosperity had never been seen before.
a car （that） can travel 150 miles an hour.（作主語）
The car that he drives can travel 150 miles an hour.
{The car can travel 150 miles an hour.這是主句部分.}
拿著the car 往后面定語從句部分（he drives）去放,應(yīng)放在 he drives 后..也就是做drive 的賓語.