The items in the list towards the end of the sentence have to be parallel.
If you try to elaborate the sentence, then it essentially says, the years…
have brought iincreased literacy (A), have brought new roads (B), and have brought improved... (C).
Point to note here—also the reason for confusion—is that
brought is the verb under which a set of things are introduced in the sentence.
‘improved’ is not a verb but an
adjective that modifies ‘farming techniques’.
It’s a quick kill after this. We can scan through the options now.
Eliminate A – alters the meaning of the sentence. Treats ‘improved’ as a verb.
Eliminate C – does not maintain parallelism.
Eliminate D – lack of parallelism. All three items must agree with each other.
Eliminate E – same as all the others; parallelism error.
Option B is the best option. Hope this helps!