The sentence states that Louis had a "long string of losses in a recent tournament," and this fact was almost certainly contributed to by his $\qquad$ chess. We need two words or phrases that fit in the blank and logically explain why Louis lost many games.

Key points:
1. Louis lost many games ("long string of losses").
2. The blank describes Louis's relationship with chess, and this contributed to his losses.

Thus, the blank should imply that Louis is not skilled or experienced at chess, leading to his losses.

Analyzing the Options
Let's evaluate each option to see if it fits the context of explaining losses.
A. an authority on
- Meaning: An expert in chess.
- Fit: If Louis were an authority (expert), he likely wouldn't have a long string of losses. This contradicts the context.
- Reject.
B. impervious to
- Meaning: Unaffected by or immune to chess.
- Fit: This doesn't make sense in the context. Being "impervious to chess" isn't a clear reason for losing games.
- Reject.

C. an amateur at
- Meaning: A beginner or non-professional at chess.
- Fit: Being an amateur could explain losing many games. This fits well.
- Select.
D. exceptional at
- Meaning: Very skilled at chess.
- Fit: If Louis were exceptional, he wouldn't lose many games. Contradicts the context.
- Reject.
E. brand new to
- Meaning: Very new to chess; just started.
- Fit: Being brand new would explain losing many games. This fits well.
- Select.
F. daunting in
- Meaning: Intimidating or overwhelming in chess.
- Fit: This could imply Louis is intimidating to others, which doesn't explain his losses. Alternatively, if it means he finds chess daunting, that could fit, but "daunting in chess" is awkward phrasing. Less clear than C or E.
- Reject.

Verifying the Best Fits
The two options that clearly explain Louis's losses are:
- C. an amateur at: Lack of skill/experience leads to losses.
- E. brand new to: Being new leads to losses.

Both imply Louis is not skilled or experienced, which aligns with the context of losing.

Why Other Options Don't Fit
- A, D: Suggest high skill, which contradicts losses.
- B: Doesn't logically connect to losing.
- F: Unclear or awkward in this context.

Final Answer
The two correct answers are $\mathbf{C}$. an amateur at and $\mathbf{E}$. brand new to.
Correct Answers: C, E