She has played a decisive role in the peace negotiations.

她在和谈中起了关键作用。

They have played a decisive role in building Silicon valley.

在硅谷建设中他们起了决定性作用。

In this sense, agriculture plays a decisive role in good or bad.

从这个意义上讲，农业的好坏起着决定性作用。

State governors, who appoint election officers, play a decisive role.

州长们，也就是任命选举官员的人，在其中扮演至关重要的作用。