Answer:
C). Strong.
Step-by-step explanation:
Tone is demonstrated as the approach or attitude that the author adopts towards a specific subject matter that is reflected by the diction and language. It assists the readers to have a perspective to look at and understand the text.
In the given sentence, the word 'assertive' conveys a dominating tone that the author adopts to portray the manager's decisive, self-assured, and insistent attitude which could be changed by replacing the word 'assertive' with 'strong.' This would shift the tone from 'forceful' to 'well-built' and 'verified' position. Thus, option C is the correct answer.