One student will need to hold the meter stick in a vertical position while the other student measures (or marks with chalk) the shadow's length.
(One student; will need; to hold the meter stick in a vertical position) Context(One student will need,List([0, 21))):(One student; will need to hold; the meter stick; L:in a vertical position)
One student will need,List([0, 21))
One student One student
will need will need to hold
to hold the meter stick in a vertical position
the meter stick L:in a vertical position