Explanation
According to the Proxy modes | Citrix Secure Web Gateway 12.1 - NetScaler document, to configure a Content Switching virtual server for implementing the Citrix Secure Web Gateway in the transparent proxy mode, the command should be:
add cs vserver < name > PROXY < ipaddress > < port >
The document also provides an example of the command:
add cs vserver swgVS PROXY 192.168.10.1 80
Therefore, the correct answer is C, which matches the format and the example given in the document. The other options are incorrect because they either use asterisks (*) instead of an IP address, or they do not specify a port number.