What is the most identifiable and secure boundary for state lines? a) secure landmark b) longitudinal and latitudinal lines c) rivers d) woodstakes

The correct answer is C) rivers.

The most identifiable and secure boundary for state lines is rivers.

Physical boundaries such as rivers are identifiable boundaries that limit or marks the natural division between states. Even between countries. That is the case for instance of the Mexican "Río Bravo" or the American "Rio Grande." It is the same river with different manes that creates a natural separation in the border with Mexico.

a.   it resulted in widespread unemployment.

radioactive dating, also known as  radioisotope dating  is a process that in  estimating the approximate  age  of  rocks. these data can be analyzed from  the studies dealing with the  decay of the radioactive elements that are present in these rocks. in nature, there are a few types of materials or atoms which are quite unstable and they spontaneously decay or breakdown to form other kinds of atoms.