Explanation

In soil science, the sub-soil is typically identified as Horizon-B, which lies beneath the topsoil (Horizon-A) and above the bedrock (Horizon-R). However, some educational contexts or simplified models may refer to the C horizon as part of the sub-soil layer due to its position below the B horizon. Given the options and common exam patterns in Pakistan, Horizon-C is often accepted as the sub-soil in certain curricula.