The correct answer is (B).
The word “devoting” means to give a lot of time and attention to something. In this case, the speaker did not properly use the time as he went on focusing on one point alone. This means that he spent too much time on one point and did not give enough time to the other points.
The other options are incorrect because they do not mean to give a lot of time and attention to something.
(A) Dilating means to make something larger or wider.
(C) Deliberating means to think carefully about something before making a decision.
(D) Diluting means to make something weaker or less concentrated.
(E) Distributing means to give something out to a number of people or places.