What causes a data migration to start on IBM Tivoli Storage Manager V6.3 Server?

A.
The amount of space that is used in the storage pool reaches the lowmiglimit.

B.
The amount of space that is used in the storage pool reaches the highmiglimit.

C.
The amount of space that is used in the storage pool reaches the low migration threshold.

D.
The amount of space that is used in the storage pool reaches the high migration threshold