Answer: Option D
Explanation: We need to see wich sentence is writen incorrectly.
Option a: ¿Quién lo conoce á ÉL?
This is written correctly.
Option b: ¿Quién conoce A MARÍA?
Here we replace the "El" for a name, "maria", this is written correctly.
Option C: Elena conoce A LOS DOS
Here again, the "subject" is at the end, si this is written correctly.
Option d: Roberto conoce PARA MARÍA Y POR ALBERTO
This is not written correctly, not only bad placed, so this is the right answer.
The right way to write this is:
Roberto conoce a María y a Alberto.