Final answer:
The process at issue is telomere replication, where nucleotides at the ends of DNA strands are lost during replication, a problem mitigated by the enzyme telomerase.
Step-by-step explanation:
The problem during DNA replication that is being illustrated with the kids in the video is most likely related to the replication of telomeres in eukaryotic chromosomes. During telomere replication, the ends of the chromosomes, called telomeres, shorten with every round of DNA replication because, on the lagging strand, there is no place for a primer to be made at the very end of the chromosome. The enzyme telomerase helps alleviate this problem by attaching to the end of the chromosome and adding nucleotides, allowing DNA polymerase to complete the synthesis of the lagging strand. Therefore, the correct answer to the question is 'b. Nucleotides at the ends of the DNA strands are lost when DNA replicates.'