Answer: Ligase
Explanation: Ligase is the enzyme responsible for synthesizing the Okazaki fragments into one continuous strand of DNA by joining the covalent bonds of the fragments together. Without ligase, the Okazaki fragments would remain as fragments of disjointed DNA segments.
The continuous strand does not require ligase as it continuously synthesizes new nucleotides in the direction of the replication fork. On the other hand, the synthesis of the lagging strand creates many fragments of DNA since DNA is being synthesized in the direction opposite the replication fork. As a result, new primers have to be continuously added so that DNA polymerase can continue replicating DNA as the replication fork widens.
Thus, a lack of ligase would result in the Okazaki fragments remaining as fragments of DNA, interfering with the synthesis of the lagging DNA strand. On the other hand, synthesis of the continuous strand can occur without issues since this strand does not need ligase as it is one whole strand from the very beginning.