When using a vSAN storage policy with FTT = 1 and FTM = Mirroring, how many witness components exist

When using a vSAN storage policy with FTT = 1 and FTM = Mirroring, how many witness components exist for a VMDK?

A. 0

B. 1

C. 2
D. 3

Reference: https://cloud0ps.wordpress.com/category/vmware-virtual-san/