D is the answer.
Q:
More people travel to Hong Kong in an average week than many other large cities experience in an entire year.
(A) More people travel to Hong Kong in an average week than many other large cities experience
(B) In an average week, more people travel to Hong Kong than to many other large cities
(C) The number of people who travel to Hong Kong in an average week is greater than that of other cities
(D) More people, in an average week, travel to Hong Kong than to many other large cities
(E) More people travel to Hong Kong in an average week than to many other large cities
Interpret:
Clearly, the meaning of the sentence is that
In a week, more people travel to Hong Kong than the number that travel to other large cities in an entire year. Now, we need to find the sentence that has no critical errors in it and states this without allowing misinterpretation.
Regarding the comparison, I must compare the # of people traveling to the number of people traveling, not to the experience of a city!
D does this.
D. The appositive "in an average week" clearly modifies the number of people (more) that travel to Hong Kong... in a week. As to the comparison: The # of people traveling to HK (more in a week) is now clearly compared to the # that travel to other large cities... in a year. The modifier errors have been removed! Both time frames are clear. The comparison is clearly stated and is valid.
Now to see why the other answers are incorrect:
(A) More people travel to Hong Kong in an average week than many other large cities experience
At a minimum, this sentence is not parallel and the comparison is not valid.
More people travel to HK... should be compared to the (number) of people traveling... Not to the experience of a city. This fails to be a valid comparison and fails in its parallelism.
(B) In an average week, more people travel to Hong Kong than to many other large cities
It is not entirely clear what "in an entire year" modifies.
The comparison starts out perfectly. We are comparing the number of people who travel to HK in a week... to the # who travel to many other large cities... OOOooops, this sounds like the comparison is to other large cities ALSO in a week. The time frame is not clear. B is not the answer.
(C) The number of people who travel to Hong Kong in an average week is greater than that of other cities
"of" other cities messes up this comparison. People are traveling "TO" HK and other cities.
The comparison is also not valid or parallel... "the number of people who travel to HK in an average week" ... is compared to "that of other cities." This fails the same way A fails.
(E) More people travel to Hong Kong in an average week than to many other large cities
This fails the same way B does. "in an average week" is now modifying "many other large cities", yet "in an entire year" is also modifying the same phrase. Confusion is the result. E does not make the coparison clear.