Select valid subnet masks:

A valid subnet mask is one that conforms to the conventions used in IP networking, particularly in the context of classful networking and CIDR (Classless Inter-Domain Routing). A subnet mask typically consists of a series of contiguous ‘1’ bits followed by ‘0’ bits.

The choice of 255.192.0.0 represents a valid subnet mask, as it can be expressed in binary as 11111111.11000000.00000000.00000000. This format correctly maintains the pattern of ones followed by zeros, indicating that the first two octets are used for the network portion, and the remaining two octets are available for host addresses.

When evaluating the other options, they do not align with the subnet mask format. For instance, 255.255.192.255 includes a '255' at the last octet, which violates the requirement for a contiguous block of '1' bits followed by '0' bits. The same principle applies to 192.0.0.0, which is more a representation of a Class C address rather than a commonly used subnet mask. Lastly, 255.255.224.0 is also a valid subnet mask, but it is not the correct