Rivers and mountains are examples of boundaries.
a. intangible
b. territory
c. tangible
d. sovereign

the power of monarchs is limited by a fundamental set of laws in a(n)
a. dictatorship
b. constitutional monarchy
c. theocracy
d. absolute monarchy

For question 1 the best fit is really option C ie tangible boundaries. This indicates they are actual physical limitations as described rather than marking a line attributed or created by humans. The answer to question 2 is option B. ie a constitutional monarchy - an example of this occurs in countries susch as the UK and Belgium.

Answer light in color; silica-rich;

The answer is d., a mountain.