E)

A) Compares land area to Britain - incorrect
B) 'of about the same size Great Britain is, but in Laos .... - awkward construction
C) 'that is about the same size as Great Britain's land area' redundant and wordy - same size as 'Great Britain would have sufficed.
Also, the remaining part of the statement is also very awkward 'but in Laos with a ...'
D) Land area comparable to the size ...oh just too awkward
E) Finally a statement that's correct - Correctly structures the comparison of the 2 Land areas.

-A

A quicker way:

Contrast here is important and hence clause with "but" is essential

Eliminate B, C and D

A--Incorrect comparison

IMO E

E but can somebody elaborate on many of whom are...