<p>Dams disrupt the interaction between a river and its banks, (which upset the habitat of aquatic insects and other organisms on which) fish depend for food.</p>
<p>Correct answer is upsetting the habitat of aquatic insects and other organisms on which.</p>
<p>WHY!? I chose an answer A. Why does the answer require a gerund? and not “which…”</p>
<p>The way it was written, it is the banks that are upsetting the habitat.</p>
<p>ahhh i see while its actually, the dams… makes sense… plus it sounds right …</p>
<p>and also, is which always used to refer to singular nouns?</p>
<p>“which” can refer to singular or plural nouns.</p>
<p>I eat eggs, which are big.</p>
<p>I eat an egg, which is small.</p>