When does c sound like s?

Circle,cease, celebrity, ceiling,celebrate.or try these:

cistern

cinder

citadel

cigarette

cilia

circa

cirrhosis

circular

cinnamon

cipher

city

civil

cecum

cedar

cephalus

celiac

celery

cellar

cement

cemetary

century

centennial

center

cerumen

cerebrum

cessation

cyberspace

cycle

cyanocobalamine

cyanosis

cyst

cytoplasm