The least effective of the following influence methods is:

A) rational persuasion
B) inspirational appeal
C) consultation
D) pressure

Pressure is the least effective influence method as it may lead to resistance and resentment from the person being pressured. It does not empower them to make a choice and may cause them to comply out of fear or obligation, rather than genuine buy-in. Rational persuasion, inspirational appeal, and consultation all involve a more collaborative and engaging approach to influence, leading to more lasting and positive results.