Given 2 keys and 3 messages you have to convert them into Cipher text.
when you are fixed a key, then all your Cipher messages are different for different messages
means it's a one-to-one function otherwise you can't get your original messages back.
Option A : is false due to while using K2 your m1 and m3 converting into same Cipher key (C2) .
Option D : is false due to while using K2 your m1 and m2 converting into same Cipher key.
Therefor your Answer should be either B or C
but in option C, only 2 messages are ciphering. There is possibility may it False.
Therefore Option B is correct.