We can harden a host by: a. Limiting physical access to it b. Turning off unnecessary services c. Installing patches d. All of the above e. None of the above

D

Explanation:

All three of A, B and C are required to harden a host. Thus, All of the above makes the best option.

Hardening simply refers to making your data impossible to be penetrated. More like bulletproof.

To do this, ensure measures like

- Regular Program cleanup

- Patches management

- service pack installation

- service or usage policies

... among others.

Cheers