The participation of the boys (was,were) essential to the success of the ex
网友回答
The participation of the boys (was) essential to the success of the ex.
这句话的主语应不是 boys 而是 participation（参加,参与）,所以用单数 was
======以下答案可供参考======
供参考答案1:
was主语是The participation ，要was
供参考答案2:
选择was，因为of the boys是The participation的定语，The participation是主语，所以用单数。