IMO D
Some hospitals have doctors that take on different duties
such as X(monitoring the wards),
Y ( to act as a guardian sounding a warning at the first sign of a patient in danger),
and Z (receiving new patients who require hospitalization )
The Usage of "such as" here is as in "for example" X,Yand Z.
Also X,Y and Z need to be maintain the parallel structure.
hence the answer shall be in lines with monitoring,acting and receiving, which zeroes in our options to D and E.
Option D rightly maintains Logical Parallelism and usage of correct idiomatic expression "to sound"In E, "acting as guardians and sounding" ,Sounding breaks the flow of the parallel structure giving a false impression that the sentence has another element to be compared X,Y,P and Z. If we try to insert P we would be resorting to Superficial parallelism. Hence eliminating Option E.also i read earlier that,
"Act" is followed by "like" to mean to behave or comport oneself and describe actions of a Person while
"Act" is followed by "as" to describe or mean the function of an inanimate object.Here "to act as guardian" in Option A,B and C make the mistake of following act by as when trying to mean a person.,viz gaurdian