您的客户要在下个月推出一部纪录片。他们有 3 个时长 30 秒的不同宣传视频，并希望确定观众最常观看到最后的广告是哪一个。 为了优先展示该广告，您会在 Display & Video 360 中采用哪种方式来优化视频广告素材？

Optimizing for "Completed views" (看完次数) directly addresses the client's goal of identifying which 30-second promo viewers watch most frequently to the end. This optimization strategy will prioritize serving the video creative that has the highest completion rate, ensuring the client can then focus their efforts on the most engaging ad. "Time on screen" is less precise as it doesn't guarantee the video was actually watched, only that it was displayed. "Conversions" are not the primary goal here; the client wants to understand ad engagement, not drive immediate actions like purchases. "Clicks" are also not the main objective; a viewer could click without watching the entire ad, which wouldn't fulfill the client's specific requirement of identifying the most-watched promo.