Should be ADE based on the document https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/js_libs_platform.htm

A, C and E are correct.
https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/js_libs_platform.htm

The <ltng:require> tag in Aura components is used to load JavaScript resources efficiently. It offers several capabilities:

B. Loading externally hosted scripts
The <ltng:require> tag allows you to specify external JavaScript files that are hosted on different domains. This is useful for including libraries and scripts from external sources.

D. One-time loading for duplicate scripts
The <ltng:require> tag ensures that each script is loaded only once. If the same script is requested multiple times, it will be loaded just once to avoid redundant network requests and potential conflicts.

E. Specifying loading order
You can specify the order in which JavaScript files are loaded using the <ltng:require> tag. This is important when the order of scripts affects their functionality or dependencies.

The other options are not directly related to the <ltng:require> tag:

A. Loading scripts in parallel
The <ltng:require> tag does not inherently support parallel loading of scripts. The loading behavior is typically sequential, especially when the script order is specified.

C. Loading files from Documents
The <ltng:require> tag does not load files from Salesforce Documents. It is designed for including JavaScript resources either externally or from static resources, but not directly from Salesforce Documents....