The answer would be C
No, no los conozco.
Since los is plural which is more than one person. Since the question was asking if you know my cousins that is more than one then los would apply to this. A and B are singular so those can be eliminated. C and D are plural but primos is masculine with an o this D would be incorrect since it is feminine. This leaves you with your final option, C which is the correct answer.
Hope this helps! :3
