The answer is A. The second one is two clauses that only need a comma for separation. The third had what needs a comma afterwards in parentheses. The last one does not even have two, which automatically makes it incorrect, as well as the information being necessary for the context of the sentence.
I<span>t provides the example of sweating sickness.
This example shows the reader that there was a disease and cause of death in Elizabethan England that does not still exist to our knowledge today. Most people probably had never heard of 'sweating sickness', so when it's presented in the passage it is effective in showing that Elizabethan ailments were different than modern ones. </span>
D. because a custom is like a tradition
