Word Choice and Formal Tone

Read the following passage and consider how the author's word choice contributes to the overall tone. Then, select the answer choice that best maintains the formal tone of the passage.

Despite the considerable challenges faced during the project, the team exhibited remarkable determination and resilience. Their ability to adapt to unforeseen circumstances was not only commendable but also inspiring.

Which of the following words, if inserted into the second sentence, would best enhance the formal tone of the passage?