To create a new data set by combining data across multiple-source properties, which Analytics 360 feature would be used?

The correct choice is roll-up properties, which play a crucial role in aggregating data from multiple source properties into a single view. This feature allows organizations to consolidate their data across various accounts or properties, enabling a comprehensive analysis of their performance as if they were one unified entity. Roll-up properties streamline reporting and data management processes, making it easier to derive insights from the combined data.

The other options do not provide the same capability. Data streams are used to collect data from a specific source, but they do not combine data from different properties. Custom dimensions allow users to define additional attributes for their data but do not facilitate the aggregation of multiple sources. Data filters help in refining the data that appears in reports but are not intended for combining data from various properties. Thus, roll-up properties are specifically designed for this purpose, making them the correct answer for creating a new dataset that integrates data across multiple source properties.