当裁判做出不公平的判罚时，观众席上立刻响起了嘘声。

The crowd let out loud ___boos when the referee made an unfair call.

万圣节时，孩子们躲在灌木丛中发出嘘声吓唬路人。

On Halloween, the kids hid in the bushes and let out loud ___boos to scare passersby.