How did seashells get into sedementary rock

Lava and other matierls luanced from a volcano and into the air are referenced as

Prices for products became more affordable as a result of new forms of ,witch got things to market faster and cheaper

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.