.net3.5 fails to be installed by default, prompting that the source file cannot be found. As shown in the figure:
It is because that Windows update service is not running.
In the Start menu, run services.msc, and press Enter to find the windows update service. The status is disabled by default; change it to Manual and enable it. Install the .net3.5 component online, and disable the windows update service as needed after the installation is complete.
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