According to PCI$-$DSS Requirement $11$: Test security of systems and networks regularly; how often should external penetraion tests be performed?

$1.$

According to PCI$-$DSS Requirement $11,$ external penetration testing should be performemed at least once every three months and after any changes to segmentation controls$/$methods$.$

$2.$

According to PCI$-$DSS Requirement $11,$ external penetration testing should be performemed at least once every six months and after any changes to segmentation controls$/$methods$.$

$3.$

According to PCI$-$DSS Requirement $11,$ external penetration testing should be performemed at least once every twelve months and after any changes to segmentation controls$/$methods$.$

$4.$

According to PCI$-$DSS Requirement $11,$ external penetration testing should be performemed at least once every eighteen months and after any changes to segmentation controls$/$methods$.$