What is the study of the history of tree rings called?

answer; belief perseverance;

answer; oxygen to the brain;

in some situations true but in others false

the secretary of defense is the principal defense policy advisor to the president. under the direction of the president, the secretary exercises authority, direction, and control over the department of defense.

as you did not provide any choices for me to choose from to give you a direct answer, this is the only information i can provide.