Fact 1: Electrocution causes harm to an organism. Fact 2: Hair dryers without built-in shock protection devices in the plug can cause electrocution. Given the two facts above, what can be done to make hair dryers safer?

OPT:
[I] remove plastic covering.
[II] immerse in water.
[III] heating liquids.
[IV] Add shock protection.
[V] converting electricity to heat.
[VI] Electric generators.
[VII] a hydraulic system.
[VIII] increase current.
The answer is:
[IV]