The correct answer is D. The lame man was laughed at by the boy.
The other options are incorrect because they do not accurately describe the relationship between the boy and the lame man. In option A, the boy is simply laughing while seeing the lame man. This does not necessarily mean that he is laughing at the lame man. In option B, the boy is laughing when he sees the lame man. This is more specific than option A, but it still does not necessarily mean that he is laughing at the lame man. In option C, the lame man is laughed by the boy. This is the passive voice version of option D, and it does not change the meaning of the sentence.
Option D is the most accurate because it specifies that the boy is laughing at the lame man. This means that the boy is making fun of the lame man, which is a negative action. The other options do not specify that the boy is laughing at the lame man, so they are not as accurate.