Insufficient data to determine frequency Steps:

• Time-base of 5 ms cm^{-1} gives time per unit length on CRO screen.
• Frequency requires period T (time for one cycle), calculated as T = (distance for one cycle in cm) × 5 ms.
• No information provided on distance between wave peaks or cycles on screen.
• Without spatial measurement of the trace, frequency f = 1/T cannot be computed. Why C is correct:
• Not enough information; no calculation supports 6.7 Hz specifically. Why the others are wrong:
• A: No basis for 6 Hz without trace details.
• B: No basis for 67 Hz without trace details.
• D: No basis for 67 kHz without trace details.

Final answer: Not enough information.