Final answer:
Six diodes are needed to convert three-phase AC power to high-efficiency DC power using a three-phase bridge rectifier. The provided answer options do not include the correct number of diodes.
Step-by-step explanation:
To convert three-phase AC power to high-efficiency DC power, a full-wave rectification process is required. The most common and efficient method of rectifying three-phase AC power is through the use of a three-phase bridge rectifier. This configuration consists of six diodes, each pair handling one of the three phases. Therefore, the correct answer to the question is none of the options provided in the question, as six diodes are needed for a full three-phase rectification.