Step 1: Identify ISI.
ISI (Indian Secret Intelligence is often confused; in context, Islamic terrorist networks) is linked to extremist elements within the Islamic community that operate to further sectarian objectives.
Step 2: Activities.
Involved in terrorism, insurgency, and destabilization; ideology is rooted in radical interpretations of Islam.
Step 3: Conclude.
\[
\boxed{\text{Islam (Option B) is associated with ISI.}}
\]