Hello!
Answer:
The blank in the sentence could be filled in with the following words:
- determined
- focused
- serious
- unwavering
- professional
Step-by-step explanation:
These words all describe the quality of someone's face who is serious about their work and who is not to be trifled with.
When someone has a determined, focused, serious, unwavering, or professional quality to their face, it is clear that they are not messing around and that they are there to get things done.