Please help I will mark you BRAINLIST

How does the molecular clock work? a. it analyzes the brain functionality of two different species.b. it examines and compares the physical characteristics of two different species.c. it illustrates relationships between two different species.d. it compares the number of mutations that exist in the dna of two different species.

Why reason best illustrates why hershey and chase chose to use viruses in their experiment?

This is so important ugh its 25 points