Which conference resource does the sixth conference use?

Refer to the exhibit. You have six IP phones configured to use MRGL_CFB. Each phone is making a conference call. Which conference resource does the sixth conference use?
Exhibit:

A. HW_CFB_1
B. HW_CFB_2
C. SW_CFB_1
D. SW_CFB_2
E. SW_CFB_3