This is a good question to test your understanding of grammatical and logical parallelism. As I have already discussed in one of my posts on parallelism, there needs to be a conjunction before the last element of the list of items being logically put in parallel, and we need to do the same for every list. This is to ensure that the lists can be clearly delineated into different lists. On the trickier GMAT questions (700+), the GMAT will often test your understanding of multiple layers of parallelism. Let us understand this through an example -

INCORRECT John eats chocolate, pizzas, bread, and likes to swim
CORRECT John eats chocolate, pizzas, and bread, and likes to swim

In the above example, we have two logical lists - namely the things that John eats, and the actions John performs. Therefore, the conjunction (and) needs to be there before the last element of both the lists.

Coming back to the question above, there are two sets of things that we are looking to put in parallel, and these need to be clearly identified:

• 1. the stuff that has been improved by the efforts - techniques, equipment, and quality of seeds
  2. efforts have improved and (have) reduced

Only option E uses the necessary conjunctions to properly identify the two lists. Every other option is missing the crucial conjunction and before the last element 'quality of seeds' of the first list.

Please let me know if anything doesn't make sense.