Correct Answer: B
Explanation:
The majority of colleagues were not convinced because explanations were not offered for the evidence. The missing word describes these explanations. Therefore, the explanations cannot be a word like ‘unconvincing’ or ‘hidden’. ‘Alternative’ is suitable for placing in the blank as it completes the meaning of the sentence as a whole. ‘Substitute’ carries the same meaning as ‘alternative’ and hence, B and D are the correct answers.