According to the phenomenon of gene segregation, the final result should be DD: DD: DD = 1: 2: 1, but this student's experimental results are not consistent with it. The reason for the failure of the experimental results is that the grabbed building blocks are not put back into the original bucket after each grab, which makes the probability of each gamete being grabbed unequal. Therefore, the captured gametes should be put back into the original barrel after each capture to ensure that each gamete is captured.

Therefore, choose: B.