Agenetic change that caused a certain hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back make possible the evolution of the tetrapod limb. this type of change is illustrative of

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?