Question

A cline: is continuous variation that follows a continuum. is variation that falls into discrete categories. describes the pattern of occurrence of trisomy 18. was used to describe human variation as early as the renaissance

Answer 1

Cline comes from the word ecoline. The term describes a series of connected populations in a species and the the gradual change in certain characteristics 
exhibited by their members.
From the given options, the one that gives definition of cline is: Cline is is continuous variation that follows a continuum.