Average bond strength in enamel adhesion:: (A) 5-10 MPa, (B) 20-50 MPa, (C) 50-70 MPa, (D) 70-100 MPa
Answer is B. Bond strength of enamel is higher than bond strength to dentin.
Enamel is 20-50 MPa.
Dentin is 15-25 MPa depending on agent used. 
Reference-Sturdevant 6th ed  Pg: 116