<p>Let's analyze the sentence:<br></p><p><strong>The recent investigation ___ [that the building may be structurally unsound due to the use of substandard materials during construction]</strong></p><p>The part wrapped with "[]" is a noun clause. <br></p><p dir="ltr">The subject of this sentence is "The recent investigation". The blank should be filled with a verb. All four choices are variations of the verb “reveal.” The key to identifying the correct answer is to tell whether the verb “reveal” is used in the right voice and the right tense. </p><p dir="ltr"><span><span>First, (B) "</span><span>is revealed"</span><span> and (C) "</span><span>was revealed"</span><span> should be eliminated since the meaning of the context suggests that the verb should be in the active voice, not the passive one. </span></span></p><p>(A) "reveals" and (D) "has revealed" are possible answers since both of them are in the active voice. Now, we need to find out which tense is more appropriate than the other. The word “recent” suggests that the investigation has been done recently and up till now has revealed something. (A) "reveals" is in the simple present tense, suggesting that the act of revealing something is a fact that happens all the time. The verb “reveal” in this tense is not so appropriate as it is in the present perfect tense. Thus, the correct answer is (D) "has revealed". </p>