Bluebook writing problem help?

Test Preparation SAT Preparation
1

<p>Can someone please help me with the #20 in test # 4 section 7 of the bluebook. </p>

<p>Social scientists A(agree that) a system B(for exchanging)
goods and services is C(not only) present but also D(of necessity) in all societies.E(no error)</p>

<p>the answers D but I dont get why, I checked the explanation online and I still don't get it, when I read it, it sounds right.</p>

2

<p>The error in this sentence occurs at (D) where there is a lack of parallelism. The prepositional phrase “of necessity” is not parallel with the earlier adjective “present.”</p>

3

<p>how should it be written then</p>

4

<p>Social scientists agree that a system for exchanging
goods and services is not only present but also necessary in all societies.</p>