The correct answer is D.
A. “I was told by somebody about the explosion in the Town Hall” is incorrect because it implies that the speaker was told about the explosion by multiple people. However, the question states that the speaker was told about the explosion by one person.
B. “I was told about the explosion in the Town Hall” is incorrect because it does not specify who told the speaker about the explosion. The question states that the speaker was told about the explosion by somebody, but it does not specify who that somebody was.
C. “I was informed that there was an explosion in the Town Hall” is incorrect because it implies that the speaker was given official notification of the explosion. However, the question states that the speaker was simply told about the explosion by somebody.
D. “I was told by somebody that there had been an explosion in the Town Hall” is the correct answer because it accurately reflects the information provided in the question. The question states that the speaker was told about the explosion by somebody, and it does not specify who that somebody was.