Audits Are Either Done Based on the Status of a System

Audits are either done based on the status of a system or application at a specific time or done as a study over a period of time that takes into account changes and processes. Which of the following pairs matches an audit type that is done over time, along with the minimum span of time necessary for it?

A) SOC Type 2, one year
B) SOC Type 1, one year
C) SOC Type 2, one month
D) SOC Type 2, six months