如果先行词在
从句中做主语且先行词是复数，则从句中的
谓语动词也要用复数。
如果先行词在从句中是作状语或者宾语的话，从句的谓语的数与先行词无关。
例如：In the playground, there is a cat which belongs to Mr White
先行词在从句中作主语，所以从句的动词要用单数。
例：In the playground, there is a cat we often play with.
先行词在从句中作宾语，这里从句的主语是we所以谓语用play.
例：In our town, there is a park where we often play games.
先行词在从句中作状语，这里从句的主语是we所以谓语用play.
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