When a surfer rides an ocean wave on her surfboard, she is actually riding on
a. a crest that is toppling over.
b. a trough of the wave.
c. the rest position of the wave.
d. a region of rarefaction.

Ateacher gives students four liquids commonly found in the kitchen - vinegar, apple juice, dish detergent, and milk - and ph indicator strips, which measure acidity. the teacher asks the students to put the liquids in order from most acidic to most basic. what type of investigation could the students conduct to determine the correct order for the liquids?