品牌提升测试的最长持续时间是多久？

The correct answer is "No maximum duration" because LinkedIn's Brand Lift Testing does not impose a strict upper limit on how long a test can run. While practical considerations like campaign flight dates and budget often dictate the duration, the platform itself allows for flexibility. This enables marketers to run tests for as long as needed to gather statistically significant data, especially for campaigns with longer sales cycles or those targeting niche audiences. The other options (six months, one year, ninety days) are incorrect as they suggest fixed maximums that do not exist within LinkedIn's Brand Lift Testing framework.