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Hello masterJ,
As mentioned in the explanation, the reason your answer was marked incorrect is due to AWS VPC restrictions on mixing RFC 1918 ranges. While 172.16.0.0/16 and 192.168.0.0/16 are valid private IP ranges under RFC 1918, AWS does not allow you to associate secondary CIDR blocks from different RFC 1918 ranges when your primary CIDR block is already within one of them.
In this case, since the primary CIDR block is 10.0.0.0/16, you cannot use 172.16.0.0/16 or 192.168.0.0/16 as secondary blocks. Please refer to the attached image.
I hope this helps! Let us know if you need further assistance.
Regards,
JR @ Tutorials Dojo
