Which tool is most likely used during a field investigation? microscope x-ray diffraction altimeter hydrometer

Most likely an altimeter,
microscopes can be too heavy to carry outside,
 x-ray diffraction is used to determine the molecular structure of a crystal so that is not likely to be helpful,
but an altimeter determines the altitude of an object on a fixed level, so that can be useful during a field investigation
hydrometers-measure gravity of liquids, probably not useful for a field investigation