C is correct. The interface fastEthernet 0/0.1 command creates a subinterface with the decimal. 1. A, B, D, and E are incorrect. A is incorrect because encapsulation dot1Q 1 sets the encapsulation for the subinterface. B is incorrect because ip address 192.168.1.1 255.255.255.0 assigns an IP address to the subinterface. D is incorrect because the subint is a command option. E is incorrect because serial interfaces can’t have subinterfaces. Solution C is correct. The interface fastEthernet 0/0.1 command creates a subinterface with the decimal. 1. A, B, D, and E are incorrect. A is incorrect because encapsulation dot1Q 1 sets the encapsulation for the subinterface. B is incorrect because ip address 192.168.1.1 255.255.255.0 assigns an IP address to the subinterface. D is incorrect because the subint is a command option. E is incorrect because serial interfaces can’t have subinterfaces..