To fix or establish clearly:控制住：清楚地固定或建立：was finally able to pin down the cause of the disease.最后终于确定病因
To force (someone) to give firm opinions or precise information:强求承诺：强迫某人提供确定意见或正确信息：The reporter pinned the governor down on the issue of capital punishment.记者强求州长在死刑问题上发表确切看法