To determine the correct statement(s) regarding transistors from the options provided, let's analyze each statement based on transistor configurations and their characteristics.

1. The doping level of emitter region is more than the base region but less than the collector region.
   • This statement is incorrect. In a bipolar junction transistor (BJT), the emitter region is the most heavily doped to provide a large number of charge carriers, ensuring efficient injection into the base. The base is lightly doped, and the collector is moderately doped (more than the base but usually not more than the emitter).
2. The CB configuration is a good current amplifier circuit configuration.
   • The Common Base (CB) configuration is not typically known for its current amplification; it is used for voltage amplification and has a current gain of less than one. Therefore, this statement is incorrect.
3. The phase difference between input and output waveforms of a CB configuration amplifying circuit is 0°.
   • This statement is correct. In a Common Base configuration, the input and output signals are in phase, meaning there is no phase difference between them (0° phase difference).
4. CC configuration transistor amplifier has higher value of input resistance and lower values of output resistance.
   • This statement is correct. The Common Collector (CC) configuration (also known as an emitter follower) offers high input resistance and low output resistance, making it suitable for impedance matching applications.

Based on the analysis:

• Statement C is correct: I/P and O/P waveforms of a CB configuration have a 0° phase difference.
• Statement D is correct: CC configuration has higher input resistance and lower output resistance.

Thus, the correct answer is C & D only.