Answer:
B. a group of organisms with one common ancestor and all its descendants in an unbroken line.
Step-by-step explanation:
A clade is a taxonomic group of organisms consisting of a common ancestor and its descendants. The members of a clade share a common ancestry, and the concept of a clade is used to organize the evolutionary relationships between species and higher-level taxonomic groups. Clades can be visualized as branches on a tree-like diagram called a phylogenetic tree, with the common ancestor at the tree's base and the descendants branching out from there.