Which circumstance should a network administrator implement only outgoing NAT towards an ISP?

Under which circumstance should a network administrator implement only outgoing NAT towards an ISP?
A. when traffic that originates inside the network must be routed to internal hosts
B. when the network has few public IP addresses and many private IP addresses that require outside access
C. when the network must route UDP traffic
D. when traffic that originates outside the network must be routed to internal hosts