Which of these would be caused by a chemical change?

a)
the formation of lava.

b)
sedimantary rock layering over time.
eliminate

c)
metamorphic rock forming from igneous.

d)
metamorphic rock eroding to form sedimentary rock.

Ascience research group is testing a new type of plant food. one trial is conducted in a controlled experiment. the data from the trial show that the plant that received the new food grew faster than the control plant. the group announces that the new plant food makes plants grow faster. what is the main weakness in this scientific claim?