What are the two reference frames currently used globally?

The correct choice identifies the two primary reference frames widely employed for global positioning and geolocation. The International Terrestrial Reference Frame (ITRF) is a highly precise system established for global positioning, utilizing satellite data, and is fundamental for various applications in geodesy, navigation, and Earth sciences. WGS84 (World Geodetic System 1984) is another critical reference frame used globally, particularly in GPS technology, which provides a consistent framework for spatial positioning.

Both ITRF and WGS84 are crucial for ensuring that geographic information is accurately represented and interoperable across various mapping and navigation technologies. This interconnection allows for a standardized approach to measuring and representing geographical data, making it essential for a multitude of applications in GIS and related fields.

The other choices refer to older or regional reference frames, which, while significant in their respective contexts, do not serve as the primary global reference frames currently in use. NAD83 and NAD27, for instance, are specific to North America, and WGS72 is an outdated system that has since been replaced by WGS84. Hence, the selection of ITRF and WGS84 reflects the contemporary and globally recognized systems used for precise location determination and spatial analysis.