1) Burst
○ "A sudden burst of sound" → Correct (a burst of sound is common).
○ "A bright burst of light" → Correct (a burst of light is also valid).
2) Blare
○ "A sudden blare of sound" → Correct (blare of sound is common).
○ "A bright blare of light" → Incorrect (blare is related to sound, not light).
3) Flash
○ "A sudden flash of sound" → Incorrect (flash is not used for sound).
○ "A bright flash of light" → Correct (flash of light is common).
Thus, "Burst" is the only word that fits both blanks; "Blare" fits only the first blank; "Flash" fits only the second blank.
Hence, the correct choice is (a) Only I.