正解:B
In Network Time Protocol (NTP), the stratum level represents the number of hops away from the authoritative time source. A stratum 1 server is directly connected to an authoritative time source, such as an atomic clock.
Each subsequent stratum level represents an additional hop in the hierarchy. For example, a stratum 2 server gets its time from a stratum 1 server, a stratum 3 server gets its time from a stratum 2 server, and so on. The higher the stratum number, the further the device is from the authoritative time source, and potentially the less accurate the time. References: Explanation of Stratum Levels & NTP