<p>if investors accept doubt then that means they shouldn’t be diffident in the first place. you’re basically finding a word that has to do with “uncertainty” and “doubt,” not any word that reasonably makes the sentence</p>
<p>The sentence starts with “Uncertainty.” That’s almost a direct definition of ambiguity. </p>
<p>This is one of those cases where you need to consider connotative meanings. “Diffident” really does not mean “doubtful,” it is more shyness. Not to mention that you would never say that you “tolerate diffidence.”</p>
<p>If you ever see any questions like this on your actual SAT, just remember that a good answer isn’t the best answer. C may work, but it’s a stretch. D fits in the sentence much better.</p>