Which of These Statements Is an Example of Kelvin-Helmholtz Contraction

Multiple Choice

Which of these statements is an example of Kelvin-Helmholtz contraction?

A) a contraction of the planet Mercury as it cooled, with consequent buckling of the surface
B) a contraction of a dense cloud of gas slowly gets hotter due to the release of gravitational energy
C) the condensation of ices (e.g., ammonia) onto dust particles in the early solar nebula
D) a contraction of a thin cloud of gas, in which the temperature remains constant due to the escape of infrared radiation