Answer:
The correct answer is letter "D": Research was too extensive.
Explanation:
Extensive research Extensive research covers many areas of study focusing on all of them at the same time. These studies could take longer to be finished due to the vast number of variables being measured. Extensive research opposes intensive research which is the study focusing on one topic only.
Even if extensive research can be time-consuming, it does not represent a big obstacle at the moment of determining the success or failure of a study. Thus, this is likely the least cause for the firm in the example failure of two product lines.