Help me with these questions! (SAT Writing)

Test Preparation SAT Preparation
1

<ol>
<li>(When Marie Curie shared) the 1903 Nobel Prize for Physics (with two other) scientists-her husband Pierre Curie and Henri Becquerel-she (had been) the first woman (to win) the prize. (No error).</li>
</ol>

<p>I chose no error. The right answer was 'had been'. WHY?</p>

<ol>
<li>Most of the sediments and nutrients of the Mississippi River (no longer) reach the coastal wetlands, a phenomenon that has (adversely) (affected) (the region's) ecological balance. No error.</li>
</ol>

<p>I chose 'the region's'. Isn't 'region's' supposed to be the same as 'region is'? There was no error in this one -.-</p>

2

<ol>
<li><p>It uses past perfect in a sentence set up to be in the preterite. It should be “became”. </p></li>
<li><p>'s can be used as a contraction of “XXX is” or as a signifier of possession/ownership.</p></li>
</ol>

3

<p>Is there an easy way of spotting the error in the first one?</p>

<p>I read on Sparknotes that “XXXs” signifies possession, and that “XXX’s” is the contraction.</p>

4

<p>^Not really. Just learn the past perfect tense and when to spot it.</p>

5

<p>Alright. Thanks!</p>