The correct answer is C.

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Explanation:

Answer choice (C) correctly describes the underlying forces of hydrogen bonding. Electronegative atoms bound to hydrogen dispropotionately pull covalently bonded electrons toward themselves, which leaves hydrogen with a partial positive character. That partial positive charge is attracted to nearby negative or partial-negative charge, such as those on other electronegative atoms. (A) is not true; hydrogen has little electronegativity and does not hold its valence electrons closely. (B) is a true statement, but does not describe the cause of hydrogen bonding. (D) is not correct; although these bonds are highly polarized, they are not ionic.