Which expression below will return the time an individual entity spent in the system in Simio, using built$-$in Simio functions $($i$.$e$.$ not user$-$defined functions$)?$

a$.$ TimeNow $-$ ModelEntity.TimeCreated

b$.$ TimelnSystem

c$.$ TimeNow $-$ TimeCreated

d$.$ ModelEntity.TimelnSystem

e$.$ TimeNow $-$ ModelEntity.TimelnSystem