Which of the following statements about idea models is not true?
a. idea models depict a concept.
b. idea models are typically used to predict natural disasters.
c. idea models are typically in the form of a graph or equation.
d. idea models are used to show the relationship between variables.

Which statement is true regarding weathering in dry environments? a) chemical weathering is absent because of a lack of humidity. b) physical weathering is usually more evident than chemical weathering. c) it is impossible to identify the type of weathering that has occurred. d) physical weathering does not play a significant role in dry environments.