Which rock is most commonly found in the highlands of the Moon?

The highlands of the Moon are primarily composed of anorthosite, which is a types of igneous rock characterized by a predominantly plagioclase feldspar mineral composition. Anorthosite is important in the lunar geological context as it is formed from the crystallization of a magma ocean that existed on the Moon in its early history. This rock type contributes to the light-colored, rugged terrain seen in the lunar highlands, contrasting with the darker basalt found in the lunar maria (the lowland plains). Anorthosite typically contains very little iron and is less dense than basalt, which contributes to its prevalence in the highlands.

In comparison, basalt is the main rock type found in the maria and forms from volcanic activity, while granite is mainly an earthbound rock not associated with lunar geology. Limestone, composed primarily of calcite, is also not found on the Moon and is instead formed in aquatic environments on Earth. Thus, the dominance of anorthosite in the lunar highlands makes it the correct answer.