The sentence describes the symphony negatively: "self-indulgent, inconsistent, and technically clumsy." However, it then states that these flaws "reflected the young composer's real but still
$\qquad$ talents." The word "but" signals a contrast. This means that despite the flaws in the symphony, the composer does have real talent, but it's not yet fully realized or refined.

We are looking for words that imply that the talent is present but not yet mature or fully developed.

Let's evaluate the options:
- A. pedestrian: Lacking inspiration or excitement; dull. This contradicts "real talents."
- B. exceptional: Unusually good; outstanding. This contradicts the "still" and the negative criticisms of the symphony, implying the talents are already fully realized.
- C. underdeveloped: Not fully grown or developed. This fits perfectly. The composer has real talent, but it hasn't reached its full potential yet.
- D. egregious: Outstandingly bad; shocking. This contradicts "real talents."
- E. immature: Having or showing a lack of maturity; childish. This also fits perfectly. It suggests the talent is real but not yet refined or sophisticated, aligning with "self-indulgent, inconsistent, and technically clumsy."
- F. ordinary: With no special or distinctive features; normal. This contradicts "real talents."

Both C. underdeveloped and E. immature accurately convey the idea that the composer's talent is genuine but has not yet reached its full potential or sophistication, which is consistent with the critical assessment of the symphony.

The final answer is $\(C, E\)$