<p>I need help with these...</p>
<p>Most major air pollutants cannot be seen, although large amounts (of them) (concentrated in) cities (are visible) (as) smog.</p>
<p>The cost of (safely disposing) of the toxic chemicals (is approximately) (five times what) the company paid (to purchase it). </p>
<p>(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.</p>
<ol>
<li><p>E (I don’t see any errors)</p></li>
<li><p>D</p></li>
</ol>
<p>“it” is referring to chemicals so it must be plural.</p>
<ol>
<li>C </li>
</ol>
<p>“had been” needs to be was. Would you say:</p>
<p>When I was born, I had been my mothers first born child.</p>
<p>To amplify on the 3rd one: had been would indicate a past time before the time of the other verb–that the being was completed before the time of the sharing. But in this sentence, the being is contemporaneous with the sharing.</p>
<p>thank you but for the first question shouldn’t it be “are as visible as smog” instead of “are visible as smog” however the answer is no error i just don’t understand why</p>
<p>Saying as visible as smog would change the meaning of the sentence. The sentence is saying that you can’t see most pollutants, but sometimes you can see them in the form of smog. Your version would mean that the pollutants are as visible as smog is, therefore the smog and pollutants are two different and unrelated things.</p>