Figure 10-13 Depicts a Strategy by Which a DNA Fragment

Figure 10-13 depicts a strategy by which a DNA fragment produced by cutting with the EcoRI restriction nuclease can be joined to a DNA fragment produced by cutting DNA with the HaeIII restriction nuclease. Figure 10-13
Note that cutting DNA with EcoRI produces a staggered end, whereas cutting DNA with HaeIII produces a blunt end.Why must polymerase be added in this reaction?

A) Polymerase will fill in the staggered end to create a blunt end.
B) Polymerase is needed to seal nicks in the DNA backbone.
C) Polymerase will add nucleotides to the end produced by the HaeIII restriction nuclease.
D) Without polymerase, there will not be enough energy for the reaction to proceed.