If two organisms are in the same clade, what can you predict about their relationship?
they are not closely related.
they share a common ancestor.
they compete for resources.
one organism evolved into the other organism.

The best answer to the stated question above is the second option.

If two organisms are in the same clade, they share a common ancestor.

What do you mean by clade?
>A clade is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single "branch" on the "tree of life"

The correct answer is -

They share a common ancestor.

Explanation:

Evidences for the common descent of living organisms (that is whether they have evolved from the same ancestor) have been elucidated through phylogenetic tree.

A clade (also called monophyletic group) is considered as a group of individual organisms, with common ancestor and its descendants. It indicates a single "branch" on the phylogenetic tree (also known as "tree of life).

Therefore, two organisms belonging to the same clade share common ancestor.

There are 2 possible answers;
A. Smaller cells use nutrients more efficiently. No wasted space etc. It's easier to live small.
B. Reproduction.