The correct answer is 5′ to 5′ triphosphate linkage.
mRNA capping is the posttrancriptional modification of messenger RNA when the nucleotide on the 5′ end is specially altered. The process is highly regulated and it creates stable and mature messenger RNA able to undergo translation. The cap on the 5’ end of mRNA consists of a guanine nucleotide connected to mRNA via an unusual 5′ to 5′ triphosphate linkage. Guanosine is methylated on the position 7 after capping.