Which bridge is the root for CIST?

Refer to the Exhibit.
Sw-1 and Sw-2 as shown in the exhibit are configured as follows:
Sw-1
admin@Sw-1# show
configuration-name juniper;
revision-level 1;
bridge-priority 4k;
msti 1 {
vlan 10;
}
msti 2 {
vlan 20;
}
Sw-2
configuration-name juniper;
revision-level 1;
bridge-priority 8k;
msti 1 {
vlan [ 10 15 ];
}
msti 2 {
vlan 20;
}

Which bridge is the root for CIST?

A.
Neither is root for CIST.

B.
Both are root for CIST.

C.
Sw-1 is the only root bridge for CIST.

D.
Sw-2 is the only root bridge for CIST.