Which must be true for metamorphism to occur?
a. the parent rock must be in solid form.
b. the parent rock must be igneous.
c. the grain size must become smaller.
d. the process must take place underwater.

Using mr smith and his id, identify two potential internal validity threats that might affect the a—b design. tell me how that threat might impact conclusions in the a—b design. note #1: you cannot use maturation (since i already did that one for note #2: there are some mr smith id threats that won’t have much impact in a single case design.