which statement about the Layer 2 topology is true?

— Exhibit –

— Exhibit —
Click the Exhibit button.
Based on the exhibit, which statement about the Layer 2 topology is true?

A.
A port on switch 3 or switch 4 towards the CST root (switch 6) is blocking traffic.

B.
A total of 64 MST instances for MST region A and region B can be configured.

C.
MSTI BPDUs are exchanged between MST regions and the CST root bridge.

D.
IST BPDUs are exchanged only between switches 1 and 2, and between switches 6 and 7.