A. The concerns about feeding the growing global population
has usually emphasized the possibility of available farmland and soil nutrients decreasing and to what extent it might,
Subject concerns does not agree with the verb has
B. The concerns about feeding the growing global population have usually emphasized whether available farmland and soil nutrients would decrease and the extent that is,
Here when we split the sentence, we notice that it is not parallel. Also each bullet should be able to stand on its own and we notice that the second bullet doesnt.
The concerns have emphasized
1. whether available farmland and soil nutrients would decrease
C. Concerns about feeding the growing global population
have usually had as its emphasis whether available farmland and soil nutrients would decrease and what that extent would be,
Have had is unnecessary as there is no other second past event to express this kind of sequencing
D. Concerns about feeding the growing global population have usually emphasized whether available farmland and soil nutrients would decrease and to what extent,
Correct
E. Concerns about feeding the growing global population
has usually had as an emphasis the possibility of available farmland and soil nutrients decreasing and to what extent it might,
Same as A.
Answer is D