C) í, iste, ió, imos, isteis, ieron
The correct demonstrative adjective for this sentences would be "este".
* Este niño en la foto es mi primo Francisco". Because "ESTE" refers to a singular male subject. If it would have been a girl, the correct option would have been "ESTA". For plurals we need to use "estos" and "esa" when it is a singular, female and we point the subject at a certain distance. "Esa es mi prima" --> That is my cousin (over there)
It’s incorrect because the verb should be in the to form, not the he she form. I hope this helps!