The answer is A.The calcium atom must bond with an atom of high electronegativity (like fluorine) because the higher electronegativity atom will bully the low electronegativity atom and take away its electrons.
These are the choices:
A. an atom with a high electronegativity, like fluorine
B. another atom with a low electronegativity, like lithium
C. another atom that would like to share electrons
D. no other atoms because it's too weak to bond with anything