In the Middle Ages, people accused of being witches were often tested by being dunked in a river or pond. If they floated to the surface, they were condemned as witches. If they sank and drowned, they were posthumously acquitted. This test obviously lacks .

validity

Explanation:

A validity test is such test that measures what it's supposed to measure. A test that returns result of individual being condemned or acquitted as a witch or not doesnt measure what it should return.

You can also determine the validity test by running another test called inter-rater reliability. Thia is done by applying or doing a series of tests to either support or reject the result gotten from a validity test.

  b.

there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.