Conversion of alternating current into direct current is called:

Explanation

Rectification is the correct answer because it specifically refers to the conversion of alternating current (AC) into direct current (DC). This process is essential in many electronic devices that require a stable DC supply from an AC source. Amplification is incorrect because it pertains to increasing the strength of a signal, not converting it. Oscillation is incorrect as it describes a repetitive back-and-forth motion, not a conversion process. Regeneration is incorrect because it is not related to electrical circuitry or processes.