In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

The spectre of growing cyber threat demands changes in the ____________________ of users of systems, a ____________________ approach to investment in hardening systems, better training __________________ computer security practices, and careful engineering of things to be connected to networks. Almost certainly it would __________________ that certain critical computers and controls are unhooked from the network, a _______________ known as 'air gapping'.