Which Noncovalent Interaction Is NOT a Possible Between CAMP and CAMP

Which noncovalent interaction is NOT a possible between cAMP and cAMP receptor protein (CRP) ?

A) an ionic interaction between an arginine and the phosphate group
B) a serine donating a hydrogen bond to N7 of adenine
C) a threonine donating a hydrogen bond to the NH₂ substituent at position 6 of adenine
D) a serine donating a hydrogen bond to a phosphate oxygen
E) a backbone NH group donating a hydrogen bond to the 2´ OH