Which of the following is a possible result of abrupt changes in wind speed and direction while flying?

Abrupt changes in wind speed and direction during flight lead to turbulence. Turbulence occurs when an aircraft encounters irregular air movements, which can be caused by various factors like atmospheric instability, terrain effects, or shear forces from wind changes. This can create a bumpy ride as the varying pressure and airflow disrupt the smooth flight path of the aircraft.

In contrast, stable flight conditions would refer to a lack of significant variability in air movement, which is the opposite of what is described in the question. Severe icing is associated with specific weather conditions, particularly in cold and moist environments, rather than changes in wind dynamics. Increased fuel efficiency is generally a function of consistent, smooth airflows that allow for optimal performance, rather than abrupt shifts in wind which tend to lead to inefficiency and increased drag on the aircraft. Thus, turbulence is indeed the direct result of the abrupt changes referred to in the question.