Rna primase synthesizes rna primer that attaches itself at the initiation point of replication. rna primer constructed during dna replication needs to be replaced because rna differs from dna. it contains instead of options for 1: adenine, cytosine, uracil options for 2: adenine, guanine, thymine

The answer is; Uracil, Thiamine

The two different structurally, with thymine having a methyl group in its ring structure which uracil lacks. DNA does not have uracil because  Cytosine can be tautamerized and deaminate to produce uracil. Uracil is recognized by repair enzyme of DNA, nicked and replaced by cytosine. If uracil were a component of DNA, the repair systems would not be able to distinguish original uracil from uracil originated by deamination of cytosine. Thymine is more stable than uracil, a requirement for DNA which stores critical cell information.

2%? i tried finding the exact sorry if it's not 100% correct ; -;